MEDICAL    >§ClnI<0>©L 


tl   OF  PHARMACY 


CHEMISTRY 
DEPARTMENT 


Oafffornia  College  of  Pharma 


WORKS  OF  ALFRED    I.  COHN 

PUBLISHED    BY 

JOHN  WILEY  &  SONS,  Inc. 


Indicators  and  Test-papers. 

Their  Source,  Preparation,  Application,  and  Tests 
for  Sensitiveness.  With  Tabular  Summary  of  the 
Application  of  Indicators.  Second  Edition,  Revised 
and  Enlarged,  ix  -f-  267  pages.  5  by  j^.  Cloth, 
$2.50  net. 

Tests  and  Reagents. 

Chemical  and  Microscopical,  known  by  their 
Authors'  Names;  together  with  an  Index  of  Sub- 
jects, iii 4-383  pages.  6  by  9.  Cloth,  $3.50  net. 

TRANSLATIONS. 

Fresenius's  Quantitative  Chemical  Analysis. 

New  Authorized  Translation  of  the  latest  German 
Edition.  In  two  volumes.  By  Alfred  I.  Cohn, 
Phar.D.  Recalculated  on  the  basis  of  the  latest 
atomic  weights,  and  also  greatly  amplified  by  the 
Translator.  2  vols.,  upwards  of  2000  pages.  6  by  9. 
280  figures.  Cloth,  $12.50,  net. 

Techno-Chemical  Analysis 

By  Dr.  G.  LUNGE,  Professor  at  the  Eidgenossische 
Polytechnische  Schule,  Zurich.  Authorized  Trans- 
lation by  Alfred  I.  Cohn,  Phar.D.  vii  +136  pages. 
5  by  7/4-  *6  figures.  Cloth,  $1.00,  net. 

Toxins  and  Venoms  and  Their  Antibodies. 

By  EM.  Pozzi-EscoT.  Authorized  Translation  by 
Alfred  I.  Cohn,  Phar.D.  vii-l-ioi  pages.  5  by  7^. 
Cloth,  $1.00,  net. 


INDICATORS  AND  TEST-PAPERS 

THEIR    SOURCE,   PREPARATION, 

APPLICATION,  AND    TESTS 

FOR   SENSITIVENESS 

A  Resume  of  the  Current  Facts  regarding  the  Action 
and  Application  of  the  Indicators  and  Test- 
papers  which  have  been  Proposed  from 
Time  to  Time,  and  are  in  Present 
Use  in  Chemical  Manipulations 

WITH   A 

TABULAR  SUMMARY  OF  THE  APPLICATION  OF  INDICATORS 


DESIGNED   FOR    THE    USE   OF  CHEMISTS, 
PHARMACISTS,    AND    STUDENTS 

California  CoHege  of  Pharmac 


BY 


ALFRED    I.  JIOHN,  PH.G. 


SECOND  REVISED  AND  ENLARGED  EDITION. 


NEW  YORK 

JOHN  WILEY  &  SONS,  INC. 
LONDON:  CHAPMAN  &  HALL,  LIMITED 


Copyright,  1899,  1902 

BY 

ALFRED  I.   COHN 


PRESS  OF 

BRAUNWORTH   &   CO. 

BOOK   MANUFACTURERS 

BROOKLYN.    N.    Y. 


PREFACE 


MUCH  has  been  written  on  indicators  within  the  last 
twenty  years  in  the  various  journals,  etc.,  devoted  to 
chemistry  and  pharmacy.  No  systematic  arrange- 
ment, however,  appears  to  have  been  made  of  the 
facts  recorded  by  a  host  of  observers,  which  would 
present  the  busy  worker  with  the  widely  scattered  in- 
formation in  the  form  of  a  succinct  yet  comprehensive 
compilation. 

The  purpose  of  this  work  is,  hence,  to  present  an 
up-to-date  resum6  of  the  knowledge  regarding  the 
various  substances  which  have  been  proposed  for  use 
from  time  to  time  as  indicators,  so  far  as  their  prep- 
aration, properties,  application,  etc.,  are  concerned. 
Such  a  resume  appears  all  the  more  desirable,  because 
of  the  increasing  value  of  titrimetric  methods,  in 
consequence  of  their  ease  and  rapidity  of  application, 
and  more  particularly  because,  with  the  increase  of 
knowledge  regarding  the  action  of  the  various  acids, 
alkalies,  and  reaction-products  on  indicators,  arises 

iii 


IV  PREFACE 

the  recognition  of  the   necessity  for  a  correct  choice 
of  the  indicator  most  suitable  for  a  given  case. 

The  subject-matter  has  been  largely  compiled  from 
the  files  of  the  various  chemical  journals,  reports  of 
the  meetings  of  chemical  and  pharmaceutical  societies, 
and  works  on  chemistry,  in  the  English,  French,  Ger- 
man, Spanish,  and  Italian  languages ;  and  it  has  been 
arranged  in  the  form  believed  to  best  meet  the  re- 
quirements of  the  chemist,  pharmacist,  and  student. 

In  the  section  devoted  to  Indicators  only  those  sub- 
stances have  been  discussed  which  are  used  purely  and 
simply  as  such ;  under  Test-papers,  however,  it  has 
been  deemed  desirable  to  include,  all  regarding  which 
any  reference  could  be  found. 

ALFRED  I.  COHN 

NEW  YORK,  July,  1899 


PREFACE  TO  THE  SECOND  EDITION 


THE  flattering  reception  accorded  the  first  edition  of 
the  Indicators  and  Test-Papers  has  encouraged  the 
author  to  publish  a  second.  In  this  the  text  has  been 
carefully  gone  over,  and  the  few  errors  incident  to  a 
first  edition  corrected.  The  entire  work  has  been 
brought  up  to  date  by  the  addition  of  an  appendix 
embodying  the  information  on  the  indicators  intro- 
duced since  the  appearance  of  the  first  edition. 

A.  I.  C. 

NEW  YORK,  January,  1902 


California  CoHege  of  Pharmac" 


TABLE  OF  CONTENTS 


PART   I 

INTRODUCTION 

PAGE 

General  Considerations I 

Correct  Choice  of  Indicators 5 

Application  of  Indicators 8 

Action  of  Indicators  in  other  than  Aqueous  Liquids 12 

Theory  of  the  Action  of  Indicators 15 

PART    II 
IN DIC A  TORS 

Alizarin 20 

Alkanin 25 

Alpha-Naphtolbenzein 29 

Azolitmin 30 

Benzaurin 34 

Benzopurpurin  B 35 

Brazil  Wood , 37 

Brazil  in 38 

Cabbage,  Red .'....  41 

Carmine.... 42 

Carminic  Acid 45 

Cobaltous  Nitrate 48 

Cochineal 49 

Coleln 54 

Congo  Red 55 

Corallin 58 

Corallin  Red 58 

v 


VI  TABLE   OF  CONTENTS 

PACK 

Curcumin 59 

Curcumin  W 62 

Cyanine 63 

Diazo-paranitraniline-Guaiacol 64 

Dimethylamidoazobenzene 65 

Diphenylamine 67 

Eosine 68 

Eosine-Methylene  Blue . '. 70 

Ethyl  Orange * 71 

Eupittonic  Acid < ...     72 

Flavescin 74 

Fluorescein 75 

Fuchsine 78 

Gallein 80 

Haematoxylin. .  . , 82 

Haematoxylon 85 

Indigosulphonic  Acid 88 

Indigo  Carmine. 89 

lodeosine 91 

lodeosine  G 93 

Iron  and  Ammonium  Sulphate 94 

Lacmoid  95 

Litmus 99 

Luteol 1 06 

Mallow 108 

Mesitylene  Quinone no 

Methyl  Orange   in 

Methyl  Orange  and  Phenolphtalein 118 

Methyl  Violet 118 

Orange-peel  Extract 120 

Para-Nitrophenol 120 

Phenacetolin 122 

Phenol  Nitrosylsulphonate 125 

Phenolphtalein 126 

Phenylenediamine,  Meta- 132 

Phyllocyanin 133 

Poirrier  Blue  €48 135 

Poly  sulphide  Solution 137 

Potassium  Bichromate 138 

Potassium  Chromate 140 


TABLE   OF  CONTENTS  Vll 


Potassium  Ferricyanide 142 

Potassium  Hydrorufigallate  (?) 144 

Potassium  Permanganate 145 

Reflecting  Galvanometer 147 

Resazurin 149 

Resorcinbenzein 151 

Rose  Coloring-Matter 152 

Rosolic  Acid,  Commercial 153 

Salicylic  Acid 157 

Santalin 159 

Sodium  Salicylate 162 

Starch 162 

Tetrabromophenolphtalein. . . . .  , 163 

Thy molphtalein  166 

Toluylene  Red 167 

Tropaeolin  OO 168 

Tropaeolin  OOO  No.  i 170 

Tropaeolin  OOO  No.  2 171 

Zinc-Iodide  and  Starch 172 

PART    III 
TEST-PAPERS 

Alkanin 176 

Azolitmin 177 

Benzopurpurin 177 

Brazilin 178 

Brucine 179 

Buckthorn 179 

Carmine 179 

Citro-Mercuric-Chloride 180 

Citro-Molybdic- Acid 180 

Citro-Potassium-Ferrocyanide  181 

Citro-Sodium-Tungstate 181 

Cobalt-  and  Methylene-Blue 182 

Cobalt  182 

Cochineal 183 

Colein 183 

Congo-Red 184 

Corrosive-Sublimate 185 


Vlll  TABLE   OF  CONTENTS 

PAGE 

Curcuma 185 

Dimethyl- Paraphenylenediamine 188 

Elderberry .- 188 

Ferment 189 

Ferrous-Sulphate 189 

Fuchsine 190 

Georgina 190 

Gold-Chloride 191 

Guaiac 192 

Guaiac-  and  Copper-Sulphate 192 

Haematoxylin 193 

Houzeau's  Ozone 194 

Huckleberry 195 

Hyacinth 195 

Indigo , 196 

Indigo-Carmine 196 

Indigo-Carmine  and  Sodium-Carbonate 196 

lodate 197 

Iris 197 

Lacmoid  198 

Lead 200 

Litmus 200 

Mallow 202 

Manganous-Chloride 203 

Manganous-Acetate 203 

Metaphenylenediamine 203 

Methyl-Orange 204 

CEnokrine 204 

Palladious-Chloride 205 

Phenolphtalein 206 

Phloroglucin- Vanillin 206 

Picro-Citric-Acid 207 

Pole-Reagent 207 

Potassio-Mercuric-Iodide 208 

Potassium-Chromate 208 

Potassium-Ferricyanide.  , 209 

Potassium-Ferrocyanide 209 

Potassium-Iodide 210 

Potassium-Iodide  and  Starch 210 

Potassium  Sulphocyanate 211 


TABLE   OF  CONTENTS  IX 

PACE 

Resazurin 21 1 

Rhubarb 212 

Rose 213 

Rosolic-Acid . 213 

Schiff s 213 

Serum 214 

Silver-Nitrate ' 214 

Starch 215 

Starch-  and  Ammonium-Persulphate 215 

Sulphanilic-Acid  and  Alphanaphtylamine  Sulphate 216 

Tannin 216 

Tetramethvl-Paraphenylenediamine 217 

Thallous- Hydrate 217 

Tropaeolin 218 

Ultramarine 218 

White-Lead 219 

Zinc-Iodide  and  Starch 219 

PART    IV 

TABLES  AND    TABULAR  SUMMARY 

Trommsdorff' s  Table,  showing  the  Sensitiveness  of  Indicators  to 
Acids  and  Alkalies 220 

Thomson's  Table,  showing  the  Hydrogen  Atoms  replaced  by 
NaOH  or  KOH  when  a  Compound  Neutral  to  the  Indicator  is 
formed 223 

Dieterich's  Table  showing  Sensitiveness  of  Various  Test-Papers.   224 

Tabular  Summary  of  Principal  Indicators. 

APPENDIX 

Alizarin  Green  B 225 

Ammoniacal  Copper  Solution 226 

Corallin-  Malachite-Green 227 

Diazoparanitraniline-  Propylmetacresol 229 

Iron  Isopyrotritarate 230 

Iron  Salicylate 232 

Patent  Blue  L 235 

Perezol 235 

Potassium  Ferrocyanide  with  Ammonium  Molybdate 238 

Sodium  Alizarinsulphonate 239 


PART  I 


GENERAL    CONSIDERATIONS 

An  indicator,  in  chemistry,  is  a  substance  used  for 
the  purpose  of  affording  ocular  evidence  regarding 
the  condition  of  acidity,  alkalinity,  or  neutrality  ex- 
isting in  a  liquid ;  or  of  indicating  the  termination  of 
a  reaction,  whereby  the  quantity  of  the  reagent,  the 
titrating  liquid,  used,  enables  the  quantity  of  the  re- 
acting substance  present  in  the  liquid  to  be  stoichio- 
metrically  determined.  In  titrimetric  determinations 
the  indicator  effects  its  object  when,  without  taking 
any  immediate  part  in  the  reaction  going  on,  it  be- 
comes affected  the  moment  the  liquid  becomes  neu- 
tral, acid,  or  alkaline,  and  indicates  this  moment  by 
a  change  of  color  or  the  formation  of  a  precipitate, 
because  of  its  having  also  entered  into  a  reaction  with 
the  reagent,  but  only  after  that  between  the  reagent 
and  the  substance  under  investigation  is  complete  and 
at  an  end. 

The  value  of  an  indicator  depends  on  its  sensitive- 
ness to  the  action  of  acids  and  alkalies,  and  on  the  dif- 


2  INDICATORS  AND    TEST-PAPERS 

ference  in  the  intensity  and  sharpness  of  change  in 
the  colors  afforded  by  them.  Many  plants  yield  col- 
oring-matters which  are  sensitive  to  the  action  of 
acids  and  alkalies,  and  many  synthetically  produced 
dyes  are  similarly  sensitive.  The  number  of  sub- 
stances that  may  serve  as  indicators  is,  hence,  a  com- 
paratively large  one.  Not  all  of  them  are,  however, 
equally  serviceable.  Some  are  not  sufficiently  sen- 
sitive ;  in  some  the  color-changes  are  not  sufficiently 
pronounced ;  in  others,  the  color-changes  cannot  be 
observed  in  colored  fluids;  the  action  of  others  is 
interfered  with,  or  even  neutralized,  by  products  of 
the  reaction  going  on,  or  by  certain  chemicals  which 
may  be  present ;  many,  again,  are  only  applicable  to 
special  purposes,  etc.  To  be  of  practical  value  for 
general  use,  therefore,  an  indicator  must  not  only  be 
sufficiently  sensitive  to  sharply  and  decidedly  show 
the  moment  when  the  liquid  passes  into  a  neutral, 
acid,  or  alkaline  state,  but  the -change  of  color  must 
also  be  rapid  and  pronounced,  the  difference  in  the 
tints  afforded  must  be  as  extreme  as  possible,  and  the 
color-changes  must  be  as  free  as  possible  from  inter- 
mediate tints,  and  be  afforded  by  a  minimum  quan- 
tity of  the  indicator. 

An  ideal  indicator  that  will  answer  for  every  pur- 
pose has  not  as  yet  been  found.  Every  one  so  far 
used  has  some  drawback,  and  no  one  can  be  relied  on 
absolutely  in  all  cases.  Litmus,  for  instance,  which 
may  be  considered  as  being  of  most  general  utility, 


GENERAL    CONSIDERATIONS  3 

may  be  used  with  organic  acids  or  ammonia,  and  also 
for  caustic  alkalies  in  hot  or  cold  liquids;  but  with 
carbonates  or  bicarbonates  the  titrations  must  be  car- 
ried out  in  boiling  liquids ;  methyl  orange,  on  the  other 
hand,  is  useful  only  in  cold  liquids,  and  when  organic 
acids  and  nitrites  are  absent ;  phenolphtalein  may  be 
used  in  hot  or  cold  liquids,  but  ammonia  or  ammoni- 
acal  salts  must  be  absent;  rosolic  acid,  again,  while 
useful  in  hot  or  cold  liquids,  cannot  be  employed 
when  ammonia  or  organic  acids  are  present;  while 
cochineal  tincture  is  applicable  in  both  hot  and  cold 
liquids,  but  only  when  acetic  acid  and  metallic  salts 
are  absent,  etc. 

When  the  chemical  characteristics  of  the  indicators 
are  closely  studied,  it  soon  becomes  apparent  that  the 
latter  possess  more  or  less  acid  properties,  as  a  rule, 
and  fall  naturally  into  three  classes,  which,  though 
fairly  distinct  from  each  other,  are  not  separated  by 
decided  lines  of  demarcation,  but  tend  to  merge,  each 
into  its  next  nearest  neighbor.  These  three  groups 
may  be  defined  as  follows : 

1.  Indicators  capable  of  forming  fairly  stable  salts. 
The  members  of  this  group  are  most  sensitive  to  alka- 
lies, and  comprise  such  indicators  as  cochineal,  congo- 
red,    dimethylamidoazobenzene,    iodeosine,    lacmoid, 
methyl  orange,  etc. 

2 .  Indicators  possessing  very  faint  acid  properties, 
and  yielding  salts  which  are  very  unstable,  and  which 
are    readily    decomposed    by    the  hydrolytic    action   oj 


4  INDICATORS  AND    TEST-PAPERS 

water.  The  individuals  of  this  class  are  particularly 
sensitive  to  acids,  and  comprise  such  indicators  as 
curcuma,  flavescin,  phenolphtalein,  etc. 

3.  Indicators  occupying  a  place  midway  between 
the  other  two  classes.  The  indicators  of  this  class 
are  somewhat  stronger  acids  than  those  of  the  second 
class,  and  are  fairly  sensitive  to  both  acids  and  alka- 
lies. The  class  comprises  such  indicators  as  fluores- 
cein,  gallein,  hematoxylin,  litmus,  phenolphtalein, 
rosolic  acid,  etc. 


CORRECT    CHOICE    OF    INDICATORS 

THE  division  into  groups,  or  classes,  enables  a  cor- 
rect judgment,  which  is  of  great  importance,  to  be 
formed  with  facility  regarding  the  proper  choice  of 
the  indicator  most  suitable  for  the  work  in  hand, 
according  to  the  acid  or  basic  radical  to  be  deter- 
mined. For  instance,  for  titrating  weak  acids,  a 
glance  at  the  various  classes  will  show  that  the  indi- 
viduals of  the  second  class  are  best  adapted  for  this 
purpose;  again,  weak  bases,  it  will  be  seen,  would  be 
best  titrated  by  the  indicators  of  the  first  class ; 
whereas  strongly  acid  or  basic  substances  would  be 
titratable  by  means  of  any  of  the  indicators. 

The  majority  of  the  indicators  are,  chemically  con- 
sidered, either  weak  acids  or  salts  of  weak  acids,  the 
remainder  being  more  or  less  basic.  In  some  the  free 
acid  is  colorless,  whereas  the  salt  is  colored,  as,  for 
instance,  in  phenolphtalein ;  in  some  the  color  of  the 
salt  lacks  intensity  to  such  an  extent  as  to  be  com- 
paratively inappreciable  in  the  dilution  in  which  titra- 
tions  are  ordinarily  effected,  whereas  the  free  base 
is  very  highly  colored,  as,  for  instance,  in  methyl 
orange ;  in  others,  again,  both  the  free  acid  and  free 

5 


O  INDICATORS  AND    TEST-PAPERS 

base  have  high  tinctorial  power  and  decided,  but 
different,  colors,  as,  for  instance,  litmus  or  lacmoid. 

The  reasons  governing  the  selection  of  an  indicator 
may  be  found  in  the  statements  just  made.  For 
instance,  the  indicators  of  class  i,  which  form  quite 
stable  compounds,  require  strong  acids  to  decom- 
pose these  compounds,  i.e.,  to  replace  the  rather 
strong  acids  combined  with  the  bases.  For  example, 
methyl  orange,  which  is,  chemically,  the  sodium  salt 
of  dimethylamidoazobenzene-sulphonic  acid,  is  quite 
stable,  and  the  fairly  strong  acid  radical  can  only  be 
partially  replaced  by  organic  acids,  like  acetic,  tar- 
taric,  lactic,  etc.,  whereas  still  weaker  acids,  like  car- 
bonic, boric,  oleic,  hydrocyanic,  etc.,  are  entirely 
unable  to  replace  it.  It  is  for  this  reason  that  the 
basic  radicals  of  salts  of  the  latter  acids  can  be  readily 
titrated  just  as  though  only  bases  were  present;  salts 
of  the  former  acids  could  not,  however,  be  titrated 
at  all,  for,  since  their  acid  radicals  can  only  partially 
replace  the  acid  radical  of  the  indicator,  the  end  reac- 
tion will  be  indefinite  because  of  a  mixture  of  colors. 

On  the  other  hand,  the  indicators  of  the  second 
class,  which  possess  but  feeble  acid  properties,  and 
whose  salts,  as  already  stated,  are  very  unstable,  are 
decomposed  by  almost  all  acids,  even  the  weakest. 
Hence,  phenolphtalein,  a  representative  of  this  class, 
would  be  serviceable  for  many  alkaloids,  such  as 
quinine,  brucine,  cocaine,  cinchonine,  and  quinidine, 
and  bases  like  aniline  and  pyridine,  because,  as  these 


CORRECT  CHOICE   OF  INDICA  TORS  ^ 

do  not  yield  a  red  color  with  phenolphtalein,  any  acid 
combined  with  the  alkaloids  or  bases  may  be  titrated 
directly  with  alkali,  just  as  if  no  alkaloid  or  base  were 
present,  but  only  free  acid. 

It  will  thus  be  seen  that  the  correct  choice  of  an 
indicator  is  of  some  importance. 


APPLICATION    OF    INDICATORS 

In  employing  an  indicator,  care  should  be  exercised 
that  a  minimum  quantity  of  the  indicator  be  used 
consistent  with  the  production  of  a  decided  color  and 
sharp  change  of  tint.  It  is  needful,  however,  that 
not  too  little  be  taken  for  the  volume  of  liquid  to  be 
titrated,  because  in  too  great  dilutions  a  decided 
difference  will  be  observed  in  the  readings,  due  to  the 
dissociation  in  the  liquid  of  the  compound  formed 
between  the  indicator  and  the  titrating  acid  or  alkali. 
This  dissociation  will  occasion  intermediate  tints,  and 
more  acid  or  alkali  than  is  normally  necessary  will 
have  to  be  added  in  order  to  secure  a  pure  monotint. 

On  the  other  hand,  an  excess  of  the  indicator  must 
also  be  avoided,  because  then  the  sensitiveness  is 
lessened.  If  too  much  is  present,  more  acid  or  alkali 
must  be  added  than  would  be  otherwise  necessary, 
because  a  minimum  would  not  convert  all  of  the  indi- 
cator into  a  salt,  or  liberate  its  free  base,  and  in  such 
a  case  intermediate  tints  would  also  be  produced  ;  and 
could  only  be  overcome  by  adding  more  titrating 
fluid,  thus  again  rendering  the  readings  inaccurate  in 
very  fine  work. 

8 


A  P  PLICA  TION  OF  IN  DIG  A  TORS  9 

In  titrimetric  operations,  therefore,  definite  quanti- 
ties of  indicator  and  titrated  solution  should  be  em- 
ployed ;  moreover,  at  least  three  blank  experiments 
should  be  made  to  determine  the  quantities  of  acid 
or  alkali,  or  even  of  both,  required  to  effect  the  color- 
changes.  The  mean  of  the  readings  so  obtained 
should  be  noted  on  the  labels  of  the  bottles  holding 
the  indicator-solutions,  and  should  be  deducted  from 
the  readings  obtained  in  practice.  New  blank  deter- 
minations should  be  made  with  every  fresh  lot  of 
indicator-solution  prepared,  because  in  many  cases 
considerable  variation  exists  between  different  lots  of 
indicators.  It  is  advisable  also  to  test  from  time  to 
time  the  sensitiveness  of  the  indicator-solutions,  be- 
cause some  are  prone  to  deteriorate  on  keeping  for  a 
length  of  time.  By  attention  to  these  details  greater 
accuracy  is  attained,  and  the  errors  due  to  personal 
equation  are  largely  minimized. 

In  performing  titrations,  shallow  porcelain  dishes 
will  be  found  most  generally  useful  in  practice.  In 
these  the  color-reactions  are  most  clearly  observed, 
and  the  end  of  the  reactions  most  readily  determined. 
The  close  of  the  reaction  may  be  considered  to  be 
reached  when  the  color  occasioned  by  a  drop  of  the 
acid-  or  alkali  solution,  as  it  falls  into  the  liquid  being 
titrated,  no  longer  changes,  but  remains  permanent, 
and  can  no  longer  be  distinguished  from  that  of  the 
liquid  in  general. 

Glass  beakers  may  also  be  used,  but  they  should  be 


10  INDICA  TORS  AND  •  TEST-PAPERS 

placed  on  a  white  sheet  of  paper,  and  a  similar  sheet 
placed  behind,  in  order  to  facilitate  the  observation  of 
the  color-changes.  The  beakers  have  the  advantage 
in  cases  where  fluorescent  indicators  are  used;  i.e., 
where  the  fluorescence  is  made  use  of  in  determining 
the  end  of  the  reaction.  On  the  other  hand,  where  it 
is  necessary  to  boil  the  titrated  liquid  to  expel  carbon 
dioxide  or  hydrogen  sulphide,  the  porcelain  dishes  are 
most  suitable  (although  the  beakers  are  used  by 
many),  because  they  are  less  likely  to  break,  and, 
which  is  more  important,  are  far  less  likely  to  yield 
traces  of  alkali  to  the  boiling  liquid,  as  many  kinds  of 
glass  are  very  prone  to  do  and  thereby  introduce  a 
source  of  error  in  the  readings.  It  is,  hence,  very 
important  that  this  point  be  not  forgotten  or  over- 
looked when  titrating  boiling  liquids. 

The  color-changes  of  indicators  are  generally  best 
observed  by  daylight.  There  are  cases,  however, 
when  artificial  light  is  the  more  suitable  for  use,  as, 
for  instance,  with  cochineal,  of  which  the  change  of 
color  from  a  yellowish-red  to  a  violet-red  is  most 
clearly  observed  by  gaslight  or  the  sodium  flame 
(see  page  53). 

Another  point  to  which  due  regard  should  be  paid 
is  the  sensitiveness  of  the  operator  to  certain  colors. 
It  is  often  found  that  in  the  case  of  some  operators 
their  eyes  become  much  more  rapidly  fatigued  by  one 
color  than  by  another.  Hence  an  indicator  should  be 
chosen,  so  far  as  is  consistent  with  the  work  to  be  done, 


APPLICATION   OF  INDICATORS  II 

which  the  operator  is  best  able  to  see  well  without 
undue  fatigue.  Where  an  extended  series  of  titra- 
tionsis  being  carried  out  it  is  even  advisable  to  change 
the  indicator  from  time  to  time  in  order  that  the  eye 
should  not  lose  its  sensitiveness  to  the  color-changes. 


ACTION    OF    INDICATORS    IN    OTHER 
THAN    AQUEOUS    LIQUIDS 

ALL  the  foregoing  considerations  have  been  based 
on  the  employment  of  aqueous  fluids  for  obtaining 
the  various  color-reactions.  Different  phenomena 
are  observed,  however,  when  other  fluids  are  used. 
It  had  long  ago  been  observed  that  when  highly  alco- 
holic fluids  were  used  great  discrepancies  were  noted 
between  the  readings  afforded  in  these  and  in  aqueous 
liquids.  It  has  been  found,  in  fact,  that  the  influence 
exerted  by  alcohol  is  sufficient  to  be  the  cause  of 
serious  errors  in  volumetric  work,  unless  due  attention 
be  given  to  the  variation  in  the  readings  caused  by 
it.  The  variation  increases  practically  uniformly  with 
the  increase  in  alcoholic  strength,  being  greatest  in 
strongly  alcoholic  liquids,  and  smallest  in  liquids  con- 
taining but  a  little  alcohol. 

The  variation  in  the  readings  may  be  readily 
proved.  For  instance,  when  cochineal,  brazilin, 
hematoxylin,  lacmoid,  or  litmus  are  used  with  alco- 
hol, an  increased  quantity  of  alkali  is  required  beyond 
what  would  ordinarily  suffice  to  afford  the  change  in 
color;  i.e.,  alcohol  appears  to  act  the  part  of  an  acid. 
On  the  other  hand,  with  methyl  orange,  dimethyl- 
amidoazobenzene,  and  the  various  tropaeolins,  a  large 

12 


ACTION   OF  INDICATORS  1 3 

excess  of  acid  is  required  above  what  usually  suffices 
to  yield  the  color-changes;  i.e.,  toward  these  indi- 
cators the  alcohol  appears  to  act  like  so  much  alkali. 

These  phenomena  have  been  recently  studied  by 
John  Waddell,  who  showed  also  that  the  addition  of 
ether,  benzene,  or  chloroform,  and  in  some  cases  of 
acetone  and  alcohol,  to  aqueous  or  alcoholic  solutions 
in  which  fluorescein,  phenacetolin,  cyanine,  phenol- 
phtalein,  paranitrophenol,  methyl  orange,  turmeric, 
lacmoid,  and  corallin  were  present  in  the  form  of 
their  salts,  caused  a  change  in  color  to  that  of  the 
free  acid  or  base.  This  change  of  color  was  shown 
to  take  place  more  readily  when  the  indicator  was 
present  in  the  form  of  its  acetate  than  when  in  that  of 
its  hydrochlorate;  and  when  in  the  form  of  its  ammo- 
nium salt  than  when  in  that  of  its  potassium  salt. 

For  instance,  a  concentrated  acetone  solution  of 
phenolphtalein  is  scarcely  colored  by  a  large  excess  of 
strong  ammonia  water;  but  the  addition  of  water 
immediately  determines  the  appearance  of  the  intense 
red  characteristic  of  alkaline  solutions. 

Methyl  orange  dissolved  in  acetic  acid  affords  a  red 
solution,  the  color  of  which  is  changed  to  yellow  on 
the  addition  of  alcohol  or  acetone,  and  restored  to  red 
again  on  adding  water. 

Cyanine  yields  a  colorless  aqueous  solution,  but  its 
acetic-acid  solution  is  changed  to  blue  on  the  addition 
of  alcohol  or  acetone,  and  the  color  is  discharged  on 
adding  water. 


14  INDICATORS   AND    TEST-PAPERS 

The  other  indicators  were  found  to  yield  similar 
reactions.  The  probable  reason  of  these  color-changes 
is  to  be  found  in  the  assumption  that  the  very  weak 
acids  and  bases,  of  which  indicators  are  constituted, 
are  very  much  less  dissociated  in  organic  solvents  than 
in  water,  and  that  their  salts  become  almost  entirely 
hydrolyzed  when  these  organic  solvents  are  added  to 
aqueous  solutions  of  the  salts,  in  spite  of  the  fact  that 
the  concentration  of  the  ions  of  the  water  is  also  reduced 
somewhat.  Hence  when  these  solvents  are  added 
they  liberate  the  free  indicator-acid  or  base,  which  ex- 
hibits its  usual  color;  and  they  will  the  more  readily 
liberate  the  indicator-acid  or  base  if  these  are  com- 
bined with  a  weak  base  or  acid.  By  observing  whether 
the  change  of  color  occurred  on  adding  the  solvents  to 
the  acid  or  to  the  alkaline  solution  of  the  indicator,  or 
to  both  solutions,  it  was  possible  to  determine  whether 
the  indicator  acts  as  an  acid  or  base,  or  if  as  both. 
From  the  observations  made,  it  was  determined  that 
phenolphtalein,  paranitrophenol,  and  turmeric  act  like 
acids;  that  cyanine,  methyl  orange,  and  lacmoid  act 
like  bases;  and  that  fluorescein,  phenacetolin,  and 
corallin  act  both  as  acids  and  bases. 

However  this  may  be,  it  more  clearly  shows  that  an 
intelligent  choice  of  an  indicator  for  the  work  in  hand, 
and  in  relation  to  the  character  of  the  fluid  employed 
and  the  salts  formed  during  the  titration,  is  exceed- 
ingly important,  and  is  not  to  be  underrated. 


THEORY  OF  THE  ACTION  OF  INDICATORS 

THE  theory  of  how  the  color-changes  are  produced 
in  indicators  has  been  the  subject  of  considerable 
study  by  a  number  of  observers,  chief  among  whom 
may  be  mentioned  Nernst  and  Ostwald.  These  color- 
changes  are  ascribed  to  the  dissociation  and  regenera- 
tion consequent  on  the  addition  of  some  foreign  sub- 
stance to  the  indicator.  It  has  been  shown  that  in 
very  dilute  solution,  compounds  undergo  dissociation, 
or  ionization,  into  their  constituent  radicals,  or  ions, 
as  they  are  called.  Compounds  yielding  hydrogen 
ions  are  termed  acids;  those  yielding  hydroxyl  (OH) 
ions  are  designated  as  bases;  and  it  is  the  color-reac- 
tions which  these  hydrogen  or  hydroxyl  ions  afford 
with  certain  dyes  which  are  utilized,  and  which  render 
the  latter  of  service  as  indicators. 

Any  compound  is  suitable  for  use  as  an  indicator, 
provided  it  possesses  acid  or  basic  properties,  and 
provided  that  when  dissociated,  or  ionized,'  its  nega- 
tive ion,  r:  anion,  has  a  color  different  from  that 
which  it  has  when  in  a  non-dissociated  state.  The 
compound  must  not,  however,  be  a  strong  acid  or 
base,  because  these  ar^  'onizable  while  in  a  free  state, 

is 


1 6  INDICATORS  AND    TEST-PAPERS 

in  which  condition  no  change  of  color  occurs  on 
neutralization.  On  the  other  hand,  again,  a  very  weak 
acid  or  base  is  more  or  less  undissociated  when  in 
solution,  and  is  ionized  only  after  conversion  into  a 
neutral  salt  by  neutralization.  For  instance,  para- 
nitrophenol,  which  is  an  acid  indicator,  exists  in  solu- 
tion in  the  form  of  undissociated,  colorless  molecules, 
yet  the  anion  is  intensely  yellow  in  color.  Paranitro- 
phenol  is,  however,  subject  to  a  slight  dissociation  in 
dilute  solution,  but  this  is  entirely  overcome  when  a 
trace  of  a  stronger  acid  is  present,  when  the  solution 
remains  colorless.  If  a  base  is  now  added,  however, 
a  highly  ionizable  salt  of  paranitrophenol  is  formed, 
and  the  solution  will  then  exhibit  the  intense  yellow 
color  of  the  ion.  Cyanine,  on  the  other  hand,  is  a 
basic  indicator,  the  ions  of  which  are  colorless, 
whereas  the  non-dissociated  salt  has  a  color — exactly 
the  reverse  as  with  paranitrophenol.  Other  indicators, 
again,  as  lacmoid  or  litmus,  exhibit  a  color  both  in 
the  ionized  and  non-ionized  state,  but  the  colors  in 
both  conditions  are  different. 

It  may  be  readily  conceived  that  the  smaller  the 
quantity  of  hydrogen  ions  or  hydroxyl  ions  required 
to  effect  a  change  of  color,  and  the  greater  the  differ- 
ence in  the  colors  produced,  the  more  sensitive  and 
useful  will  the  substance  be'  for  the  purposes  of  an 
indicator.  In  addition,  its  value  will  also  be  dependent 
on  its  dissociability.  For  instance,  supposing  the 
indicator  to  be  a  very  weak  acid,  it  will  be  easily 


THEORY  OF   THE  ACTION  OF  INDICATORS      IJ 

understood  that  another  acid  of  moderate,  or  even 
small,  ionization  will  readily  yield  up  hydrogen  to  it, 
and  so  afford  the  color-change  on  its  passage  from  the 
ionized  to  the  non-ionized  state.  Such  a  weakly  acid 
indicator  could,  therefore,  be  expected  to  be  partic- 
ularly useful  for  titrating  weak  acids,  like  acetic,  tar- 
taric,  etc.,  but,  on  the  other  hand,  be  suitable  for 
strong  bases  only,  because  with  weak  ones  it  would 
form  weak  salts  readily  dissociable  by  the  hydrolytic 
action  of  the  solvent.  This  dissociation  would  thus 
yield  mixed  colors  which  would  tend  to  render  the 
final  color-change  difficult  of  accurate  determination. 
As  an  example  take  phenolphtalein,  which  is  a  weakly 
acid  indicator,  and  which  is  non-dissociated  and  color- 
less when  in  the  acid  state.  Its  alkali  salt  is,  how- 
ever, immediately  ionized  as  soon  as  it  is  formed,  the 
red  color  of  the  ion  then  becoming  apparent,  only 
again  to  disappear  on  the  addition  of  the  slightest  ex- 
cess of  an  acid  because  of  the  liberation  of  the  phenol- 
phtalein. Now,  while  the  fixed  alkalies  readily  yield 
ionizable  salts  with  phenolphtalein,  ammonia  does 
not,  because  it  is  too  weak  a  base/^r  se  to  yield  with 
the  indicator  a  salt  which  is  stable  in  very  dilute  solu- 
tions, and  moreover  a  considerable  excess  would  be 
required,  in  consequence,  to  overcome  the  hydrolytic 
action  of  the  water.  Thus  is  accounted  the  imper- 
fect and  incomplete  change  of  color  of  phenolphtalein 
when  ammonia  or  ammoniacal  salts  are  present,  and 


1 8  INDICATORS  AND    TEST-PAPERS 

why  the  color  is  in  fact  only  visible  when  a  consider- 
able excess  of  the  base  is  added. 

Methyl  orange,  on  the  other  hand,  is  a  moderately 
strong  acid  indicator,  and  its  ion  is  yellow,  whereas 
the  non-ionized  indicator  is  red.  Methyl  orange  dis- 
sociates very  readily  in  dilute  solutions,  and  is  hence 
prone  to  yield  a  mixed  color,  between  red  and  yellow. 
The  addition  of  a  trace  of  a  stronger  acid  than  it,  les- 
sens the  ionization,  and  restores  the  red  color;  a 
trace  of  alkali,  again,  yields  a  highly  ionizable  salt, 
when  the  yellow  color  of  the  ion  is  at  once  seen. 
When  a  weak  and  but  slightly  ionizable  acid  is 
added  to  the  methyl-orange  solution,  the  hydrogen 
ions  of  the  acid  given  up  in  excess  of  what  is  re- 
quired for  neutralization  are  insufficient  to  yield 
enough  of  a  non- ionized  salt  to  afford  a  decided  red 
color;  hence,  unless  an  excess  of  such  a  weak  acid  is 
added,  a  decided  reaction  is  unobtainable.  This  ex- 
plains why  methyl  orange  is  unserviceable  for  titrat- 
ing weak  organic  or  other  acids.  With  bases,  how- 
ever, the  case  is  different,  as  with  these  the  indicator 
yields  definite  salts,  even  with  weak  bases.  These 
salts  are  but  little  prone  to  be  hydrolyzed,  and  are, 
hence,  capable  of  yielding  sharp  end-reactions. 

Precisely  similar  considerations  also  apply  to  basic 
indicators;  i.e.,  for  titrating  weak  acids  a  highly  ion- 
ized indicator  is  most  serviceable,  whereas  weak  bases 
require  an  indicator  which  is  as  weakly  basic  as 
possible. 


THEORY   OF   THE  ACTION   OF  INDICATORS      IQ 

The  characteristic  action  of  the  acids  and  alkalies 
on  plant  pigments  and  dyes  has  also  been  explained 
by  F.  Mohr  by  the  mechanical  theory  of  affinity. 
According  to  the  theory,  the  acids  have  a  molecular 
oscillation  different  from  that  of  the  alkalies;  the  oscil- 
lations of  the  former  are  few  in  number  and  of  con- 
siderabje  amplitude,  whereas  those  of  the  latter  are 
many  and  narrow.  Mohr  assumes  that  the  acid  and 
alkali  impart  each  its  own  motion  to  the  sensitive  pig- 
ment. Since  it  is  assumed  that  the  colors  also  only 
exist  on  the  theory  of  molecular  vibration,  the  final 
color  is  directly  referable,  hence,  to  these  vibrations. 
It  has  been  shown  that  in  the  spectrum  the  greatest 
number  of  the  oscillations  of  color-waves  are  found  at 
the  red  end,  and  beyond  it.  Since  it  may  be  optically 
shown  that  the  red  rays  oscillate  less  rapidly  than  do 
the  violet  ones,  the  amplitude  of  their  vibrations  must 
be  greater,  in  order  to  account  for  the  excess  of  heat 
evolved  by  them.  From  this  it  follows,  then,  that 
those  substances  which  changp  the  colors  to  red 
(acids)  have  similarly  few  vibrations  but  of  consider- 
able amplitude, .  and  those  which  restore  the  colors 
(alkalies)  numerous  vibrations  of  small  amplitude. 
The  neutralization  is  the  act  wherein  the  dissimilar 
vibrations  are  made  uniform  in  number  and  in  ampli- 
tude; at  the  same  time  the  vibrations  are  in  part 
converted  into  heat  which  is  given  off  during  neutrali- 
zation. 


PART  II 
INDICATORS 


ALIZARIN 

CeH4.2(CO).C6H2(OH)a 

ALKALIES  =  Purplish-red  ACIDS  =  Yellow 

Synonyms:  Dioxyanthraquinone;  Dihydroxyanthra- 
quinone;  Schaal's  Indicator. 

Source  :  Alizarin  was  first  found  in  the  roots  of  Rubia 
tinctorum  Lin.,  madder,  a  herbaceous  perennial 
indigenous  to  the  Levant  and  Southern  Europe, 
and  cultivated  in  France,  Holland,  and  Asia  Minor. 
It  was  first  isolated  and  named  by  Robiquet  and 
Colin  in  1826,  although  Kuhlmann  in  1823  showed 
the  existence  of  a  crystalline  coloring-matter  in 
madder. 

Alizarin  does  not  exist  in  the  roots  as  such,  but 
in  the  form  of  ruberythrinic  acid  (Rochleder's),  a 
glucoside  which,  on  boiling  with  acids,  yields  ali- 
zarin and  a  glucose,  as  follows:  • 

C..H..O,,  =  C..H.O.+  C.H..O.+  H,0 

ruberyihrinic  acid  alizarin  glucose 

In  1847  Schunck  isolated  from  madder  a  bitter 
principle  which  he  named  rubian,  but  which  Roch- 
leder  considered  to  be  an  impure  ruberythrinic 

20 


ALIZARIN  21 

acid  having  the  formula  C16H16O8.  This  substance 
was  also  shown  to  be  a  glucoside  which,  on  boiling 
with  acids  or  alkalies,  yielded  alizarin  and  a  glu- 
cose, presumably  as  follows : 

2C..H..O.  +  6H,0  =  C..H.O.  +  3C.H..O. 

rubian  alizarin  glucose 

Alizarin  was  also  obtained  synthetically  by  Grabe 
and  Liebermann  in  1868  from  anthracene,  by  first 
converting  this  substance  into  anthraquinone,  and 
the  latter  then  into  anthraquinone  dibromide  (or 
dichloride),  and  finally  heating  the  dibromide  (or 
dichloride)  with  concentrated  potassa-lye ;  the  ali- 
zarin-potassa  formed  was  then  dissolved  in  water, 
and  the  alizarin  precipitated  by  adding  an  acid. 

More  recently  it  has  been  shown  that  alizarin 
is  also  formed  on  heating  phtalic  anhydride  with 
pyrocatechin  and  sulphuric  acid  to  a  temperature 
of  150°  C.  The  reaction  is  expressed  as  follows: 

C6H4(CO)20  +  H2C6H2(OH)3  =  C6H4(CO)2.C«Ha  OH)2  +  H2O 
phtalic  anhydride          pyrocatechin  alizarin 

Preparation :  The  process  generally  employed  for 
making  alizarin  is  that  patented  in  1869  by  Perkin, 
simultaneously  with,  yet  independently  of,  Grabe, 
Liebermann,  and  Caro.  This  process  depends 
upon  the  conversion  of  pure  anthraquinone  into 
anthraquinone  monosulphonate,  this  latter  being 
then  converted  into  a  sodium  salt.  One  part  of 
this  salt  is  then  mixed  with  3  parts  of  sodium  hy- 


IN DIC A  TORS 

drate,  a  little  water  and  potassium  chlorate  added, 
and  the  mixture  then  heated  for  several  days  at  a 
temperature  of  from  180°  to  200°  C.  in  closed  ves- 
sels under  pressure.  The  mass  is  then  dissolved  in 
water  and  decomposed  by  hydrochloric  acid,  the 
precipitated  alizarin  being  finally  well  washed  with 
distilled  water. 

It  had  been  the  accepted  view  for  a  long  time 
that  it  was  the  anthraquinone  disulphonate  which, 
on  fusion  with  the  potassa,  yielded  the  alizarin. 
It  was  pointed  out  by  Perkin,  however,  in  1876, 
that  this  view  was  erroneous,  and  that  the  disul- 
phonate was  converted  into  isopurpurin  and  flavo- 
purpurin,  but  that  it  was  the  monosulphonate 
which  yielded  the  alizarin.  On  fusing  the  anthra- 
quinone monosulphonate  with  potassa,  the  sulpho 
group  is  replaced  by  hydroxyl,  oxyanthraquin- 
one  being  formed.  This  latter,  however,  in  the 
strongly  alkaline  mass,  is  rapidly  oxidized  to  ali- 
zarin, small  quantities  of  oxyanthraquinone  -sul- 
phonic  acid  and  alizarin -sulphonic  acid  being 
simultaneously  formed. 

Rochleder  obtained  the  alizarin  by  preparing  an 
aqueous  extract  of  madder,  and  precipitating  with 
lead  acetate.  The  lead  precipitate,  containing  ali- 
zarin, purpurin,  fat,  and  lead  salts  of  other  acids 
present  in  madder,  is  suspended  in  water  and  de- 
composed by  a  current  of  hydrogen  sulphide.  The 
precipitate,  now  containing,  besides  lead  sulphide, 


ALIZARIN  23 

only  the  alizarin,  purpurin,  and  fat,  is  filtered  off 
and  boiled  with  alcohol.  Water  is  then  added  to 
the  alcoholic  solution,  and  precipitates  a  yellow, 
gelatinous  mass  which  soon  becomes  crystalline 
flocks  consisting  of  alizarin  and  the  fat,  the  pur- 
purin remaining  in  solution.  The  fat  is  next  re- 
moved by  washing  with  cold  ether,  and  the  alizarin 
is  finally  recrystallized  from  hot  ether. 

L.  Vilmorin  obtained  alizarin  by  heating  garancin 
(obtained  by  the  action  of  hot  sulphuric  acid  on 
ruberythric  acid)  two  or  three  times  with  an 
aqueous  solution  of  pure  ammonia  alum,  evaporat- 
ing to  dryness  the  filtered  orange-red  extract,  and 
powdering  the  dry  residue.  This  is  then  boiled 
with  absolute  alcohol  or  carbon  disulphide,  and  the 
alizarin  crystallized  from  the  hot,  filtered  liquid. 

Properties :  Alizarin  crystallizes  from  alcohol  in  the 
form  of  long,  transparent,  brilliant,  reddish-yellow 
or  orange  colored  prisms  with  3  molecules  of  water 
of  crystallization.  The  crystals  have  a  bitter  taste, 
and  are  difficultly  soluble  in  water,  more  so  in  boil- 
ing water;  soluble  in  alcohol,  ether,  carbon  disul- 
phide, volatile  and  fatty  oils,  and  in  benzene,  with 
yellow  color.  At  100°  C.  the  crystals  lose  their 
water  of  crystallization;  they  melt  at  about  2i5°C., 
and  solidify  on  cooling  to  a  solid,  reddish-brown 
crystalline  mass;  they  sublime  at  from  215°  to 
225°  C.  as  golden-yellow,  shining  prisms  having  a 


I-  INDICA  TORS 

reddish  reflection.  With  concentrated  sulphuric 
acid  alizarin  yields  a  dark,  yellowish-brown  solu- 
tion, precipitated  by  water.  Boiled  with  dilute 
nitric  acid  it  is  converted  into  oxalic  and  phtalic 
acids,  as  follows: 

C..H.O.  +  2H.O+0,.  =  C.H.O.  +  3C,H,0. 

alizarin  phtalic  acid  oxalic  acid 

On  boiling  with  ferric  nitrate  or  chloride,  only 
phtalic  acid  is  formed. 

Alizarin  is  colored  violet  in  ammoniacal  vapors, 
and  dissolves  in  solutions  of  ammonia  or  of  alkali 
carbonates  with  a  violet-purple  color.  Alizarin 
dissolved  in  aqueous  solutions  of  an  alkali  affords  a 
solution  which,  at  certain  concentrations,  possesses 
a  deep  purple  color  by  transmitted  light,  and  a 
pure  blue  by  reflected  light.  When  greatly  di- 
luted, the  color  of  the  solution  is  uniformly  violet, 
and  on  adding  an  acid  the  alizarin  is  precipitated 
as  orange-colored  flocks. 

Alizarin  is  soluble  in  a  hot  solution  of  alum,  but 
precipitates  again  on  cooling.  With  alumina  and 
zinc  oxide  it  yields  handsome,  red,  insoluble  lakes; 
with  ferric  oxide  it  gives  a  violet  or  black  lake,  and 
with  red  acetate  a  bright  purple  one.  Its  alcoholic 
solution  yields  with  ferric  acetate  a  dark  purple, 
with  cupric  acetate  a  light  purple,  and  with  stan- 
nous  chloride  and  ammonia  a  bright  red,  pre- 
cipitate. 


A  LA' AN  IN  25 

Application:  Alizarin  solution,  for  use  as  an  indi- 
cator, is  prepared  by  boiling  an  excess  of  alizarin  in 
potassa  solution,  with  a  drop  of  carbolic  acid  added, 
and  filtering  off  the  excess  of  alizarin.  Alkaline 
solutions  are  colored  red,  acid  solutions  yellow. 

In  using  this  indicator  it  is  found  best  in  practice 
to  supersaturate  the  acid  with  standard  alkali  and 
titrate  back  with  acid. 

ALKANIN 

C16H1404 

ALKALIES  —  Blue  ACIDS  =  Red 

Synonyms:  Anchusin  ;  Alkannin ;  Pseudalkannin ; 
Alkanna  Red;  Anchusic  Acid. 

Source :  Alkanin  was  first  obtained  by  Pelletier,  in 
1818,  from  the  bark  of  the  root  of  Anchusa  tinc- 
toria  L.  (dyer's  alkanet),  one  of  the  Boraginaceae 
found  growing  in  the  Grecian  Archipelago  and  in 
Southern  Europe.  Pelletier  obtained  it  in  an 
impure  state,  however,  and  named  it  "anchusin"; 
he  calculated  its  formula  to  be  C17H20O4.  Later  on 
it  received  the  name  "anchusic  acid,"  because  of 
its  acid-like  properties,  as  it  was  found  to  yield 
neutral  compounds  with  alkalies  and  alkaline  earths, 
blue  in  color  and  soluble  in  alcohol  and  in  ether. 

Preparation:  Bolley  and  Wydler  were  the  first  to 
obtain  alkanin  in  a  pure  condition,  in  1847.  They 


26  INDICA  TORS 

obtained  it  as  a  dark-red,  amorphous,  resinous, 
brittle  mass,  by  exhausting  finely  comminuted 
alkanet  root  with  alcohol  after  previous  treatment 
with  water  and  drying.  The  alcoholic  extract  was 
acidulated  with  hydrochloric  acid,  the  alcohol  then 
evaporated,  and  the  residue  exhausted  with  ether; 
the  ethereal  solution  was  then  washed  by  shaking 
with  water,  and  the  ether  finally  evaporated.  They 
assigned  to  it  the  formula  C36H40O8.  These  observ- 
ers were  unable  to  confirm  the  statements  previously 
made  regarding  the  acid-like  properties  of  alkanin. 
and  hence  simply  named  it  "  alkanna  red." 

Carnelutti  and  Nasini,  however,  appear  to  have 
shown  that  alkanin  does  possess  the  properties  of  a 
weak  acid.  They  obtained  the  coloring-matter  by 
exhausting  commercial  alkanin  with  petroleum 
ether,  treating  the  latter  with  weak  potassa  lye, 
repeatedly  shaking  the  indigo-blue  solution  with 
ether,  which  removes  an  onion-red  substance,  and 
finally  precipitating  the  pure  alkanin  by  a  current  of 
carbon  dioxide.  The  precipitated  alkanin  was  then 
dried  in  a  vacuum,  dissolved  in  ether,  and  the  solu- 
tion filtered  and  evaporated.  Alkanin  so  obtained 
was  found  to  possess  the  formula  C1BH14O4,  which  is 
the  one  now  generally  accepted. 

Commercially,  alkanin  is  obtained  by  exhausting 
the  dried,  coarsely  ground  root-bark  by  percolation 
with  benzin,  evaporating  the  percolate  to  a  small 
^bulk  on  a  water-bath  at  a  temperature  of  from  .60° 


ALKANIN  27 

to  80°  C.,  and  spreading  the' residue  on  glass  plates 
to  dry. 

Lepage  obtained  the  alkanin  by  exhausting  the 
alkanet-root  bark  with  carbon  disulphide,  evaporat- 
ing the  solvent,  and  treating  the  residue  with  a 
2-per-cent.  sodium-hydrate  solution  at  a  tempera- 
ture of  100°  C.  From  the  filtered  indigo-blue  solu- 
tion so  obtained  the  alkanin  is  precipitated  by 
hydrochloric  acid  in  slight  excess,  and,  after  stand- 
ing for  about  24  hours,  is  filtered  off,  washed  with 
distilled  water,  and  dried. 

When  using  alcohol  for  extracting  the  alkanin  it 
is  necessary  to  slightly  acidulate  it  with  hydrochloric 
acid  before  evaporating  the  solvent,  because,  al- 
though the  alcoholic  solution  of  alkanin  does  not 
change  color  on  heating,  the  alcoholic  extract  of  the 
alkanet  root  does,  and,  on  evaporation,  yields  a 
blackish-green  residue  which  partially  dissolves  in 
water  with  a  brown  color,  and  leaves  an  insoluble 
portion  which  yields  to  ether  a  substance  to  which 
the  name  of  "  alkanna  green  "  has  been  given,  and 
which,  according  to  Bolley  and  Wydler,  is  formed 
from  alkanin  by  the  replacement  of  one  molecule  of 
carbon  dioxide  in  the  latter  by  one  molecule  of 
water. 

Properties:  Alkanin  occurs  as  a  dark-red,  amorphous, 
resinous  powder,  or  amorphous  masses  of  metallic 
luster.  C.  J.  S.  Thompson  obtained  from  5.25$  to 
6.02,^  from  the  root-bark. 


28  INDICA  TORS 

Alkanin  is  insoluble  in  water,  but  is  soluble  in 
alcohol,  ether,  ligroin,  chloroform,  benzin,  benzene, 
carbon  disulphide,  acetic  acid,  and  in  oils  generally, 
yielding  solutions  having  a  handsome  red  color 
changed  to  blue  by  alkalies.  It  is  also  soluble  with 
a  blue  color  in  solutions  of  the  alkalies,  from  which 
it  is  precipitated  by  acids  in  the  form  of  brownish- 
red  flocks.  Concentrated  sulphuric  acid  dissolves 
it  with  a  blue  color;  nitric  acid  oxidizes  it  to  oxalic 
and  succinic  acids,  and  so  does  also  a  solution  of 
bromine  in  alkalies.  Alkanin  melts  at  60°  C.,  and 
sublimes  when  carefully  heated,  yielding  violet 
fumes  which  condense  to  form  light  flocks. 

With  alkalies  and  alkaline  earths,  alkanin  yields 
blue  compounds  soluble  in  alcohol  and  in  ether;  its 
alcoholic  solution  yields  with  lead  subacetate  a  gray- 
ish-blue precipitate ;  with  stannous  chloride,  a  car- 
mine-red one;  and  with  mercuric  chloride  a  flesh- 
colored  precipitate,  whereas  that  obtained  with 
stannic  chloride  is  violet  in  color.  Concentrated 
ammonia  converts  alkanin  into  alkanna  green. 

Application  :  Alkanin  is  used  principally  in  the  form 
of  test-paper,  a  red  and  a  blue  being  made. 
These  are  described  under  Test-Papers. 


A  LPHA  -  NA  PH  TOLBENZEJN  29 

ALPHA-NAPHTOLBENZEIN 

2(CaH6.C)0.4(C10H8.OH) 

ALKALIES  =  Green  ACIDS  =  Reddish-yellow 

Preparation :  Alpha-naptholbenzem  is  obtained  by 
the  interaction  of  2  molecular  weights  of  alpha- 
naphtol  and  I  molecular  weight  of  benzotrichloride. 
In  practice  it  is  found  advisable  to  add  sufficient 
benzene  to  moderate  the  reaction,  which  begins 
at  the  ordinary  temperature,  and  may  even  be- 
come violent.  The  addition  of  the  benzene  also 
enables  a  much  purer  product  to  be  obtained. 
After  standing  for  24  hours,  the  reaction  is  brought 
to  a  close  by  warming  the  mixture  to  30°  to  40°  C.  ; 
the  benzene  and  excess  of  benzotrichloride  (if  any) 
are  then  removed  by  a  current  of  steam.  The  residue 
is  purified  by  repeatedly  dissolving  it  in  soda-lye 
and  precipitating  with  hydrochloric  acid ;  the 
product  is  finally  washed  with  distilled  water  and 
dried. 

Properties :  Alpha-naphtolbenzein  occurs  as  a  brown 
powder,  insoluble  in  water,  'but  soluble  in  alcohol. 
Its  formula  is  as  follows: 

2(C.H1.C)0.4(C1.H..OH). 

With  alkalies  it  yields  a  green,  with  acids  a  red- 
dish-yellow color. 


30  IN  DIG  A  TORS 

Application  :  Alpha-naphtolbenzein  was  proposed  by 
Zaloziecki  as  an  indicator. 

It  is  exceedingly  sensitive  to  carbonic  acid,  and 
is,  hence,  inapplicable  for  carbonates  ;  otherwise,  it  is 
equal  to  phenolphtalein  in  sensitiveness,  and  re- 
sembles the  latter  in  action  excepting  that,  on 
adding  an  acid  to  a  carbonate,  the  change  of  color 
occurs  before  the  acid  salt  is  formed. 

It  acts  with  mineral  acids,  hydrogen  sulphide, 
sulphurous  acid,  and  organic  acids  like  phenol- 
phtalein. 

Alpha-naphtolbenzein  is  much  more  sensitive  to 
acids  than  to  alkalies,  hence  it  is  best  to  always  add 
an  excess  of  alkali  and  titrate  back  with  decinormal 
acid.  One  drop  of  a  decinormal  acid  or  alkali 
suffices  to  effect  a  distinct  change  from  green 
to  orange  with  acid,  or  orange  to  green  with 
alkali. 

For  use  a  i-per  cent  alcoholic  solution  is  made; 
of  this  from  10  to  20  drops  are  added  to  100 
Cc.  of  the  liquid  to  be  titrated. 


AZOLITMIN 

C7H7NO4 

ALKALIES  =  Blue  ACIDS  =  Red 

Source :    Azolitmin   is   the    chief    coloring-matter    of 
litmus  (which  see).      It  was  first  described  by  Kane 


AZOLITMIN  31 

in  1841,  who  found  it  in  litmus  besides  earthy 
matter  and  three  other  coloring  matters — erythro- 
lein,  a  purplish-red  fatty  matter  soluble  in  ether 
and  yielding  a  purple-colored  solution  with  am- 
monia; erythrolitmin,  a  red,  crystalline  substance 
insoluble  in  ether,  but  soluble  in  alcohol,  the  color 
of  the  solution  being  changed  to  blue  by  alkalies; 
and  spaniolitmin,  a  light-red  substance  soluble  in 
water,  and  present  in  but  very  small  quantity. 

Azolitmin  does  not  exist  ready-formed  in  the 
lichens  from  which  litmus  is  prepared,  but  is 
believed  to  result  from  the  oxidation  of  orcin, 
C7H8O,,  a  colorless  principle  isolated  by  Robiquet 
in  1829  from  various  species  of  lichens.  Orcin,  in 
the  presence  of  dry  ammoniacal  air,  remains  un- 
changed, but  if  moisture  is  also  present,  it  rapidly 
takes  up  nitrogen  and  oxygen,  and  becomes  con- 
verted into  orcein,  C7H7NO, ,  a  purple  pigment, 
while  water  is  eliminated.  The  reaction  which 
takes  place  is  expressed  as  follows: 

C.H.O.  +  NH.  +  0,  =  C,H,NO,  +  2H.O 


orcin 


When,  however,  besides  ammonia,  potassa  (or 
soda)  is  simultaneously  permitted  to  act  on  the 
orcin,  a  further  oxidation  occurs,  and  the  product 
of  the  reaction  is  no  longer  purple  or  violet  in 
color,  but  blue.  A  potassium  (or  sodium)  com- 
pound has  been  formed  which,  on  decomposition 


32  INDICA'J'OKS      • 

with  an  acid,  yields  a  red  coloring-matter,  azolit- 
min.  The  higher  oxidation  may  be  expressed  as 
follows : 

C,HeO,  +  NH,  +  O.  =  C,K,NO.  +  2H,O 

orcin  azolitmin 

Preparation :  The  process  followed  by  Kane  for 
obtaining  azolitmin  was  to  exhaust  powdered  litmus 
with  water,  and  then  to  mix  with  the  liquid  some 
fine,  washed  sand.  The  mixture  was  then  evap- 
orated on  a  water-bath,  sufficient  hydrochloric  acid 
added  to  yield  a  decidedly  red  solution  after  the 
carbon  dioxide  had  been  driven  off,  and  the  evap- 
oration continued  to  dryness.  The  residue  was 
then  washed  with  water,  and  again  dried  on  the 
water-bath.  The  particles  of  sand  were  then  freed 
from  their  covering  of  pure  azolitmin  by  treatment 
with  a  weak  ammonia,  and  the  azolitmin  obtained 
from  its  solution  by  precipitation  with  sulphuric 
acid. 

According  to  Wartha,  litmus  is  macerated  with  95- 
per  cent,  alcohol  for  two  days,  and  then  collected  and 
dried.  It  is  then  macerated  in  distilled  water  for  24 
hours,  filtered,  and  the  filtrate  evaporated  on  a  water- 
bath.  The  residue  is  next  digested  with  successive 
portions  of  absolute  alcohol  containing  I  percent,  of 
acetic  acid,  each  portion  being  evaporated  before 
treatment  with  the  next.  By  this  means  the  residue 
is  freed  from  all  moisture,  and  is  enabled  to  be 


AZOLITMIN  33 

more  readily  dried  and  powdered.  The  brown, 
dry  powder  is  next  exhausted  with  the  alcohol 
and  acetic-acid  mixture,  a  scarlet  red  pigment, 
yielding  a  purplish-red  color  with  ammonia,  being 
thus  removed.  The  insoluble  residue  is  now  dis- 
solved in  water,  the  solution  filtered  and  then  evap- 
orated, alcohol  being  added  several  times  during  the 
evaporation  in  order  to  remove  every  trace  of 
acetic  acid.  The  residue,  azolitmin,  is  finally  dried 
and  powdered. 

Stolba  impregnates  washed  linen  with  a  litmus 
extract,  and  then  plunges  it  into  a  5-  or  lo-per-cent. 
sulphuric  acid,  whereby  the  azolitmin  is  precipitat.ed 
on  the  fibers.  The  material  is  then  washed  with  pure 
water,  and  finally  treated  with  weak  ammonia,  and 
the  pure  azolitmin  finally  obtained  by  neutralizing  the 
ammoniacal  solution  with  sulphuric  acid,  collecting, 
washing,  and  drying. 

The  quantity  of  azolitmin  present  in  litmus  varies 
considerably.  D.  R.  Brown  examined  7  samples  of 
litmus,  and  obtained  on  an  average  4.6  <f0  of  azolit- 
min ;  two  of  the  samples,  however,  were  found  to 
contain  over  13  <fc  of  azolitmin. 

Properties :  Azolitmin  occurs  as  a  dark,  reddish- 
brown,  amorphous  powder  or  as  scales.  It  is  but 
slightly  soluble  in  water,  and  is  insoluble  in  alco- 
hol or  ether.  With  alkalies  it  yields  blue  com- 
pounds readily  soluble  in  watei. 


34  INDICA  TORS 

Tests  :  The  sensitiveness  of  azolitmin  is  determined 
by  adding  0.5  Cc.  of  a  i-per-cent.  aqueous  solution 
of  the  pigment  prepared  by  means  of  a  few  drops  of 
centinormal  alkali,  to  100  Cc.  of  distilled  water, 
and  observing  how  much  centinormal  hydrochloric 
acid  is  required  to  change  the  color  to  red,  and 
then  testing  again  to  find  how  much  centinormal 
potassium-hydrate  solution  is  required  to  restore  the 
blue  color.  With  good  azolitmin,  1.2  Cc.  of  centi- 
normal acid,  and  3  Cc.  of  centinormal  potassa, 
should  more  than  suffice. 

Application :  Azolitmin  is  used  in  the  form  of  a 
solution  made  by  dissolving  i  Gm.  of  the  pigment 
in  100  Cc.  of  water,  just  sufficient  centinormal 
potassa-solution  being  added  to  effect  a  distinct 
blue  color.  (For  details  of  application  see  Litmus). 
Azolitmin  Test-Paper  is  also  prepared,  and  is 
exceedingly  sensitive.  (See  under  Test-Papers). 

BENZAURIN 

C8HB.C.2(CBH«).OH.O 

ALKALIES  =  Violet  ACIDS  =  Yellow 

Synonym :     Phenolbenzein. 

Preparation  :  Benzaurin  is  prepared  by  heating  2 
molecular  weights  of  phenol  with  i  molecular 
weight  of  benzotrichloride  on  a  water-bath.  After 
the  reaction  is  over,  the  excess  of  phenol  is  removed 
by  a  current  of  steam,  and  the  benzaurin  purified 


BENZOPURP  URINE   B  35 

by  repeatedly  treating  it  with  warm  solutions  of 
sodium  or  potassium  sulphite,  precipitating  by 
adding  hydrochloric  acid,  and  then  collecting  and 
drying  the  precipitate.  The  reaction  is  as  follows: 

C«H5.CC13  -f  2C«H6.OH  =  C.H..C.2(C.H4).OH.O  -f  3HC1 
benzotricliloride  benzaurin 

Properties  :  Benzaurin  occurs  as  hard,  red  crusts, 
presenting  a  metallic  reflection.  It  is  only  slightly 
soluble  in  water,  but  readily  soluble  in  alcohol, 
ether,  and  in  glacial  acetic  acid,  yielding  yellow 
solutions.  It  is  insoluble  in  benzene,  and  melts  at 
100°  C.  With  alkalies,  benzaurin  yields  a  violet 
color,  changed  by  acids  to  yellow. 

By  reducing-agents  it  is  converted   into  dioxytri- 
phenylmethane. 

Application  :  Like  other  phenol  derivatives  of  ben- 
zotrichloride. 

BENZOPURPURINE    B 

(C.H,08.(CHsN)a.N,.(C,oIVa.(NH,.SO,Na), 
ALKALIES  =  Brownish-red  ACIDS  —  Bluish-violet 

Synonym  :  Sodium  Orthotolidine-disazobinaphtyla- 
mine-sulphonate. 

Source  :  Benzopurpurine  B.  is  prepared  by  the  ac- 
tion of  I  molecular  weight  of  ortho-tolidine  on  2 
molecular  weights  of  betanaphtylamine-sulphonic 
acid,  and  the  conversion  of  the  resulting  product 
into  the  sodium  salt. 


36  1NDICA  TORS 

Properties :  Benzopurpurine  B.  was  discovered  in 
1885  by  Duisberg.  Its  formula  is  (C6H3)5(CH3.N2)2 : 
(C10HB)2(NH,.SO3Na)2,  and  it  occurs  as  a  brown 
powder  yielding  an  orange-red  to  brownish-red 
solution  with  water.  The  color  of  the  solution  is 
unchanged  by  alkalies,  but  is  changed  to  a  blue  or 
violet  by  acids. 

Application  :  Benzopurpurine  B.  was  recommended 
by  Storch  as  the  most  useful  of  the  tetrazo  dyes, 
and  as  being  superior  to  Congo  red  as  an  indicator. 
Its  aqueous  solution  affords  an  excellent  reagent  for 
free  acids;  and  the  solution,  made  violet  by  means 
of  an  acid,  is,  according  to  Storch,  one  of  the  most 
sensitive  of  indicators  for  alkalies,  known.  Even 
the  slightest  traces  of  free  ammonia  in  the  atmos- 
phere suffice  to  change  the  color  of  paper  impreg- 
nated with  a  solution  of  Benzopurpurine  B.  from 
bluish-violet  to  red.  The  indicator  may  be  used 
for  estimating  ammonia  in  the  presence  of  pyridine, 
as  titration  with  hydrochloric  acid  will  indicate  the 
total  base  ;  a  second  titration  with  litmus  or  tro- 
paeolin  OOO,  on  which  pyridine  has  no  effect,  will 
show  the  ammonia  present,  and  the  difference  will, 
hence,  equal  the  pyridine.  If  very  much  pyridine  is 
present,  however,  the  indications  are  apt  to  be  un- 
reliable. 

In  general  the  indicator  may  be  used  like  phenol- 
phtalein  ;   and  it  is  more  sensitive  than  litmus. 


BKAZ1L    WOOD  37 

BRAZIL   WOOD 

ALKALIES  —  Purplish-red  ACIDS  =  Yellow 

Synonyms:    Fernambuco  ;  Pernambuco  ;  Red-Wood. 

Source :  Brazil  wood  is  a  red  dye-wood  obtained 
from  several  species  of  Ccesalpinia  found  in  South 
America  and  in  the  West  Indies.  The  chief  species 
yielding  the  commercial  wood  are  Cczsalpinia 
echinata  Lam.  (Gmlandina  echinata  Sprengel),  C. 
crista,  C.  brasiliensis  Lin.,  and  C.  vesicaria.  A 
species  of  red-wood  closely  allied  to  the  Brazil  wood 
is  also  obtained  from  the  Ccesalpinia  sapan  L., 
Sapan  (or  Japan)  wood. 

Brazil  wood  has  been  long  used  for  dyeing  pur- 
poses, and  has  of  late  years  been  recommended  as 
an  indicator,  in  the  form  of  a  decoction,  or  in  the 
form  of  a  solution  of  the  crystalline  principle, 
brazilin,  present  in  the  wood,  and  upon  which  the 
value  of  the  wood  as  a  dye  depends  (see  Brazilin). 

Preparation  :  Brazil-wood  test  solution  may  be  pre- 
pared by  boiling  50  Gm.  of  the  comminuted  heart- 
wood  with  2  50  Cc.  of  water  for  half  an  hour,  replacing 
the  loss  by  evaporation  from  time  to  time.  After 
the  mixture  has  cooled,  it  is  strained,  the  residue 
washed  with  water  until  100  Cc.  of  liquid  are 
obtained,  and  25  Cc.  of  alcohol  then  added. 

Properties  :  The  color  of  the  solution  is  changed  to 
an  orange-yellow  by  acids,  and  almost  disappears 


38  INDICA  TORS 

on    dilution;    caustic  alkalies  and    their  carbonates 
produce  a  purplish-red  color. 

Stannic  chloride  gives  with  the  decoction  a  red 
precipitate  ;  iron  oxide  a  dirty-red  to  brown  com- 
pound ;  and  chromium  oxide  yields  a  brown  com- 
pound which,  on  the  addition  of  potassium  chro- 
mate  to  the  decoction,  is  deposited  as  a  dark 
precipitate.  On  adding  alum  to  the  decoction, 
the  latter  is  colored  red,  but  yields  no  precipitate 
until  a  basic  alkali  carbonate  is  added,  when  a  red 
lake  is  deposited.  A  similar  lake  is  obtained  on 
boiling  Brazil-wood  decoction  with  aluminum 
acetate. 

Application  :  Brazil-wood  test  solution  is  used  like 
Brazilin  (which  see). 

BRAZILIN 

C,0H1406  (C,«H1405?) 

ALKALIES  =  Purplish-red  AciDS  =  Yellow 

Synonym:    Brasilin. 

Source  :  Brazilin  is  obtained  from  several  species  of 
Caesalpinia,  principally  C.  brasiliensis  Lin.  and  C. 
echinata  Lam.,  but  is  also  found  in  Sapan  (or  Japan) 
wood,  C.  sapan  L. 

Brazilin  was  first  isolated  by  Chevreul  in  an  im- 
pure condition,  and  was  considered  by  Gerhardt  to 
be  identical  with  hematoxylin,  a  view  not  generally 


BRAZILIN  39 

accepted  because  of  the  difference  in  the  colors  ex- 
hibited by  the  compounds  of  the  two  substances. 

Preisser,  however,  in  1844,  succeeded  in  isolat- 
ing, from  the  inner  and  less  colored  portions  of  the 
wood,  the  brazilin,  in  the  form  of  colorless  acicular 
crystals,  the  solution  of  which  became  yellow  on 
standing  and  exhibited  bright-red  margins  at  the 
surface,  and  which,  on  boiling,  became  a  handsome 
carmine-red  and  deposited  on  evaporation  handsome 
bright-red  needles,  which  he  named  brazilein ;  this 
he  believed  was  formed  from  brazilin  by  oxidation 
of  the  latter  in  the  presence  of  an  alkali,  as  fol- 
lows: 

CJOH1A+0  =  C,0H,A  +  H10 

brazilin  brazilein 

Later  investigations  also  seemed  to  make  it  ap- 
pear probable  that  brazilin  is  formed  from  a  gluco- 
side  contained  in  the  wood,  but  this  has  not  as  yet 
been  shown  to  be  a  fact. 

Preparation:  Brazilin  is  generally  obtained  during 
the  preparation  and  storage  of  the  commercial  ex- 
tract of  Brazil  wood  used  in  dyeing,  in  the  form  of 
a  deposit  of  dark,  brownish-red  crusts  consisting  of 
brazilin  and  its  lime  compound.  These  crusts  are 
either  dissolved  in  boiling  5-  to  lO-per-cent.  alcohol 
with  the  addition  of  some  hydrochloric  acid  and  zinc 
dust,  or  they  are  carefully  washed  with  a  5-per-cent. 
hydrochloric  acid  and  then  extracted  with  12-per- 
cent, alcohol  and  the  brazilin  crystallized. 


40  INDICA  TORS 

Properties  :  The  appearance  of  brazilin  varies  accord- 
ing as  it  is  crystallized  from  dilute  or  concentrated 
solutions.  From  the  former  it  is  obtained  as  com- 
pact, amber-yellow,  rhombic  crystals  containing 
I  molecule  of  water  of  crystallization ;  from  the 
latter  it  crystallizes  as  white,  silky,  felted  needles 
containing  ij-  molecules  of  water  of  crystallization, 
which  is  driven  off,  however,  at  a  temperature  of 
80°  C. 

Brazilin  is  soluble  in  alcohol,  water,  and  in 
ether,  has  a  sweetish  taste,  and  on  heating  sub- 
limes partly  unchanged.  On  dry  distillation  it 
yields  resorcin.  Nitric  acid  converts  it  into  trini- 
troresorcin.  On  exposure  to  air  and  light  it?  solu- 
tion rapidly  becomes  orange-colored. 

Brazilin  possesses  the  properties  of  a  weak  acid, 
and  yields  with  alkalies  soluble,  purplish-red  com- 
pounds affording  solutions  which  are  decolorized 
by  zinc  dust,  sunlight,  sulphurous  acid,  and  by  hy- 
drogen sulphide;  the  color  of  the  solutions  is 
changed  by  acids  to  yellow. 

With  the  earths  and  oxides  of  the  heavy  metals, 
brazilin  forms  insoluble  compounds.  Caustic  alkalies 
and  their  carbonates  yield  a  purplish- red  color  with 
brazilin  solutions,  and  with  alum  a  red  lake  is 
formed. 

Brazilin  is  extremely  sensitive  to  light  and  air, 
by  which  it  is  rapidly  darkened,  becoming  orange- 


CABBAGE,  RED  41 

colored,  or  even  red.  It  must  be  preserved,  hence, 
in  carefully  stoppered,  opaque  vials. 
Application  :  Brazilin  and  decoction  of  Brazil  wood 
have  been  found  to  be  among  the  most  sensitive  of 
indicators,  and  especially  serviceable  for  titrating 
alkaloids,  with  which  other  indicators  yield  indis- 
tinct colors,  and  particularly  for  quinine,  atro- 
pine,  brucine,  and  cocaine. 

The  indicator  is  inapplicable  where  sulphurous 
acid  or  hydrogen  sulphide  are  liberated,  as  these 
destroy  the  color  of  the  solution. 

A  test-paper  is  also  used,  and  is  described  under 
under  Test-papers. 

CABBAGE,    RED 

ALKALIES  —  Green  ACIDS  =  Red 

Source  :  The  red  cabbage  is  a  variety  of  the  Brassica 
oleracea,  which  has  been  brought  under  cultivation 
from  stock  originally  found  wild  on  the  coast  of 
England  and  the  Mediterranean  as  well  as  in  Con- 
tinental Europe,  and  known  as  Wild  Cabbage,  or 
Sea  Cabbage. 

Preparation :  A  tincture  of  the  leaves  of  the  red 
cabbage  is  made  by  comminuting  the  leaves,  and 
exhausting  them  with  water  or  diluted  alcohol. 

Properties  :  The  tincture  of  the  leaves  is  violet  in 
color.  The  color  is  changed  to  green  by  alkalies, 
and  to  red  by  acids, 


42  INDICA  TORS 

Application:  Tincture  of  red  cabbage  may  be  ap- 
plied for  all  titrimetric  processes,  and  is  quite  sensi- 
tive, even  to  Ammonia.  A  paper  impregnated 
with  the  tincture  is  also  quite  sensitive.  It  is  but 
seldom  used. 

CARMINE 
ALKALIES—  Purplish-red          ACIDS  =  Yellowish-red 

Source  :  Carmine  is  the  pigment  obtained  from  the 
dried  female  insect,  Coccus  cacti,  Lin.  It  was  first 
isolated  (and  named)  by  Pelletier  and  Caventou  in 
1818,  by  treating  cochineal  with  boiling  ether  to 
remove  the  fat,  then  exhausting  with  alcohol  so 
long  as  any  color  was  extracted,  distilling  off  the 
greater  bulk  of  the  alcohol,  and  allowing  the  resi- 
due to  evaporate  spontaneously.  The  impure  car- 
mine so  obtained  was  then  treated  with  cold  alco- 
hol, which  dissolved  the  carmine  but  left  the  fatty 
matter.  From  its  solution  the  carmine  was  then 
precipitated  by  adding  an  equal  volume  of  ether. 
The  carmine  so  obtained  is,  however,  impure,  and 
it  was  only  in  1847  that  Warren  de  la  Rue  suc- 
ceeded in  obtaining  the  pure  carmine  in  the  form  of 
carminic  acid  (which  see). 

Preparation  :  Commerci-al  carmine  is  generally  pre- 
pared by  a  process  similar  to  the  following:  Pow- 
dered cochineal  is  boiled  with  40  times  its  weight 
of  water  for  15  minutes,  and  £  of  its  weight  of 


CARMINE  43 

powdered  alurn  is  added.  The  mixture  is  next 
boiled  for  3  minutes  longer,  and  then  set  aside, 
when  the  carmine  precipitates,  and  is  removed  by 
filtration.  On  allowing  the  mother  liquor  to  stand 
for  several  days,  a  second  deposit  of  carmine  is 
obtained,  which,  however,  is  not  of  as  good  a  color 
as  that  first  obtained. 

The  celebrated  process  of  Madame  Cenette  is  as 
follows:  Powdered  cochineal  is  boiled  with  75 
times  its  weight  of  water  for  two  hours ;  then  -^T  of 
its  weight  of  potassium  nitrate  is  added,  and  the 
whole  boiled  for  3-  minutes  longer,  and  finally  •§•  of 
its  weight  of  oxalic  acid  added,  and  the  mixture 
boiled  for  another  10  minutes.  The  liquid  is  then 
allowed  to  clarify  by  depositing  for  4  hours, 
when  the  clear  liquid  is  decanted  into  shallow  glass 
vessels  and  set  aside  for  three  weeks;  the  deposited 
carmine  is  then  separated  from  the  supernatant 
liquid  and  dried  in  the  dark. 

Properties  :  Carmine  occurs  in  the  form  of  small, 
bright-red  lumps,  soluble  in  ammonia  water,  and 
yielding  a  deep-red  solution,  the  color  of  which  is 
changed  to  a  yellowish-red  by  acids.  It  consists 
chiefly  of  carminic  acid,  but  contains  also  alumina, 
lime,  other  organic  acids,  and  a  protein  compound, 
according  to  Liebermann. 

Carmine  solution  is  not  decolorized  by  sodium 
sulphite ;  on  boiling  with  lime-water  it  is  colored 
violet. 


I 


44  IN DIC A  TORS 

Tests  :  Carmine  is  frequently  adulterated,  according 
to  Donath,  not  only  with  starch,  alumina,  and 
brick-dust,  but  also  with  baryta,  zinc,  and  lead 
lakes,  and  certain  azoclyes.  The  impurities  are  left 
behind  on  dissolving  the  carmine  in  ammonia. 

Equal  quantities  of  the  sample  and  of  a  known 
carmine  are  heated  in  porcelain  crucibles,  and  the 
odors  compared :  That  from  pure  carmine  resem- 
bles the  odor  evolved  on  heating  proteins,  while 
that  from  eosine-lake  will  have  a  distinct  bromine 
odor,  and  that  from  paeonin-lake  will  smell  like 
phenol.  On  incineration  the  adulterated  prepara- 
tions will  also  yield  more  ash. 

Colorimetric  comparisons  may  also  be  made  be- 
tween the  sample  and  a  known  carmine,  solutions 
of  both  being  similarly  made  by  the  aid  of  a  small 
quantity  of  ammonia,  and  compared  in  two  similar 
burettes. 

Application  :  Carmine  is  used  in  a  manner  similar  to 
that  of  cochineal  (which  see). 

Alkaline  Carmine  Solution  is  also  used  in  tit- 
rimetry.  It  is  prepared  by  dissolving  carmine  in 
soda  lye.  For  use  as  an  indicator  I  Cc.  of  this 
solution,  previously  decolorized  by  the  addition  of 
sufficient  hypobromite  solution,  is  added  to  the 
liquid  to  be  titrated. 

Alkaline  carmine  solution  is  very  sensitive  to  at- 
mospheric oxygen.  With  it,  carbonates  of  the 
alkalies  are  best  titrated  in  warm  solutions;  and 


CA  JRMINIC  A  CID  45 

carbonic  acid  gas  is  not  so  disturbing  as  when  litmus 
is  used.  The  change  is  very  sharp  and  bright,  par- 
ticularly with  pure  alkalies  or  acids. 


CARMINIC  ACID 

Ci7  H  i  (jOj  0 

ALKALIES  =  Purplish-red          ACIDS  =  Yellowish-red 

Source  :  Carminic  acid  is  the  true  coloring-matter  of 
the  dried  female  insect,  Coccus  cacti  L.,  cochineal 
(which  see). 

Preparation  :  Carminic  acid  was  first  obtained  by 
Warren  de  la  Rue  in  1847,  by  exhausting  powdered 
cochineal  with  boiling  water,  and  precipitating  the 
filtered  solution  with  lead-acetate  solution  acidulated 
with  acetic  acid.  The  precipitate  was  washed  with 
water,  and  then  decomposed  by  a  current  of  hydro- 
gen sulphide,  while  suspended  in  water.  After  filter- 
ing, the  filtrate  was  again  precipitated  by  lead- 
acetate  solution  and  the  precipitate  decomposed  by 
hydrogen  sulphide.  The  filtrate  now  obtained  was 
evaporated  in  vacuo,  the  residue  dissolved  in  boil- 
ing alcohol,  and  a  little  ether  added  to  precipitate 
nitrogenous  matter,  the  solution  again  filtered,  and 
finally  evaporated. 

Ordinarily  carminic  acid  is  obtained  by  first  treat- 
ing cochineal  with  ether,  and  then  exhausting  the 
residue  with  successive  portions  of  boiling  alcohol, 


46  INDICATORS 

which,  on  cooling,  deposits  a  part  of  the  acid,  and 
yields  the  remainder  on  spontaneous  evaporation. 
It  is  then  freed  from  adhering  fatty  matter  by  dis- 
solving in  alcohol  and  adding  an  equal  quantity  of 
ether.  The  pure  carminic  acid  is  deposited  in  the 
course  of  a  few  days. 

Properties  :  Carminic  acid  occurs  as  a  red  or  brownish- 
red  amorphous  powder,  or  crystals,  readily  soluble 
in  .water  and  in  alcohol,  but  difficultly  soluble  in 
ether. 

Its  formula  is  CnH18O10.  It  is  soluble  in  con- 
centrated sulphuric  acid  and  in  hydrochloric  acid 
without  decomposition,  but,  on  boiling  with  diluted 
sulphuric  acid,  it  yields  a  coloring-matter,  carmine 
red,  and  a  sugar,  according  to  the  following  reac- 
tion: 

C,,H,.010  +  2H,0  =  C,,H,,0,  +  C.H..O. 

carminic  acid  carmine  red 

Carminic  acid  is  hence  considered  to  be  a  gluco- 
side.  It  has  the  properties  of  a  weak,  dibasic  acid, 
and  forms  easily  soluble  salts  with  the  alkalies,  but 
forms  insoluble  violet  or  purple  salts  with  the  alkali 
earths,  earthy  metals,  and  metals  generally. 

Chlorine,  bromine,  and  iodine  decompose  it,  and 
nitric  acid  converts  it  into  oxalic  and  nitro-coccic 
acids.  Fused  with  potassium  hydrate  it  yields 
oxalic  and  succinic  acids  and  coccicin. 

The   aqueous   solution    is   faintly  acid,  and   of   a 


CARMINIC  ACID  47 

yellowish-red,  the  color  being  changed  by  alkalies 
to  a  purplish-red.  Nascent  hydrogen  decolorizes 
the  solution,  but  the  color  is  restored  on  contact 
with  the  air. 

Schutzenberger  believes  carminic  acid  to  be  a 
mixture  of  at  least  two  acids,  one  being  the  true 
carminic  acid,  having  the  formula  C9HeO6,  and  in- 
soluble in  a  mixture  of  alcohol  and  ether;  the 
other,  oxycarminic  acid,  C9HBO7,  and  soluble  in  a 
mixture  of  alcohol  and  ether. 

Tests:  i  Gm.  of  carminic  acid  should  completely  dis- 
solve in  2  Cc.  of  water;  the  addition  of  20  Cc.  of  95- 
per-cent.  alcohol  to  the  solution  should  cause  no 
noticeable  precipitation. 

A  simple  method  of  estimating  the  value  of  car- 
minic acid  is  by  colorimetric  comparison.  This  is 
accomplished  by  dissolving  equal  quantities  of  a 
preparation  of  known  quality  and  the  one  to  be 
tested,  in  equal  volumes  of  water,  solution  being 
facilitated  by  adding  a  few  drops  of  ammonia. 

The  sensitiveness  of  carminic  acid  is  tested  by 
adding  0.5  Cc.  of  a  i-per-cent.  aqueous  solution  of 
carminic  acid  to  100  Cc.  of  water,  and  observing 
how  much  centinormal  ammonia,  or  centinormal 
hydrochloric  acid,  is  required  to  effect  changes  in 
color.  A  good  preparation  will  not  require  more 
than  0.6  Cc.  of  the  acid,  0.8  Cc.  of  the  ammonia, 
or  2.8  Cc.  of  centinormal  sodium  hydrate. 


48  1NDICA  TORS 

Application:  Carminic  acid  is  used  in  titrimetric  oper- 
ations like  cochineal  (which  see).  It  is  now  being 
frequently  used  in  microscopy  as  a  stain,  although 
carmine  is  more  generally  used. 

Carminic  acid  is  far  more  sensitive  to  bicarbonates 
of  alkali  earths  than  is  litmus.  According  to  H.  N. 
Draper  it  yields  a  reaction  with  alkalies  in  solutions 
of  i:  1,400,000;  and  the  reaction  is  only  slightly, 
influenced  by  carbonic-acid  gas. 

Carminic  acid  has  also  been  lately  recommended 
as  a  precipitant  of  albumins  and  proteoses.  It  is 
claimed  to  be  exceedingly  sensitive,  I  part  of  albumin 
in  90,000  parts  of  solution  being  readily  detected. 

COBALTOUS   NITRATE 

Co(NO3),.6H2O 

Synonyms  :  Normal  Cobalt  Nitrate;  Neutral  Cobalt 
Nitrate. 

Preparation  :  Cobaltous  nitrate  is  prepared  by  dis- 
solving metallic  cobalt,  cobalt  oxide,  CoO ;  cobalt 
hydrate,  Co2(OH)6;  or  cobalt  carbonate,  CoCO3 ;  in 
nitric  acid,  evaporating  the  solution,  and  crystal- 
lizing from  the  concentrated  solution  on  cooling. 

Properties  :  Cobaltous  nitrate  occurs  in  the  form  of 
red  prisms  or  monoclinic  plates,  >  which  are  deli- 
quescent in  moist  air,  but  permanent  in  dry  air, 
and  which  melt  at  a  temperature  below  100°  C. 
At  a  higher  temperature,  cobaltous  nitrate  melts  to 


COCHINEAL  49 

form  a  viscid,  green  liquid,  and  on  strongly  heating, 
nitrogen  monoxide,  NO,  is  evolved,  cobaltic 
oxide,  Co2O3,  remaining. 

Application  :  Cobalt  nitrate  has  been  recommended 
by  G.  C.  Stone  as  an  indicator  in  the  volumetric 
determination  of  zinc  by  titration  with  potassium 
ferrocyanide.  The  cobalt  solution  should  be  quite 
dilute,  and  a  drop  of  it  placed  on  a  white  porcelain 
plate,  just  touching  a  drop  of  the  solution  to  be 
tested.  If  the  drops  touch  but  do  not  mix,  the  end- 
reaction  is  marked  immediately  by  a  greenish  line 
at  the  juncture  of  the  two  drops.  The  best  strength 
of  the  potassium-ferrocyanide  solution  was  found  to 
be  about  3  per  cent. 

COCHINEAL 

ALKALIES  =  Violet  ACIDS  =  Yellowish-red 

Source:  Cochineal  is  the  dried  female  insect, 
Coccus  cacti  Lin.,  one  of  the  Hemiptera  first  found 
living  on  various  species  of  cactus  in  Southern 
Mexico,  Guatemala,  and  Honduras,  and  later  on  in- 
troduced into  the  West  Indies,  East  Indies,  Spain, 
Algiers,  Teneriffe,  and  Malta. 

The  insect  is  gathered  some  time  after  being 
fecundated,  and  is  killed  by  immersion  in  boiling 
water,  exposure  to  steam,  or  by  drying  in  a  hot  oven 
or  on  heated  plates.  The  last-mentioned  treatment 
is  believed  to  yield  the  finest  product,  known  as 


5C  IN DIC A  TOKS 

(l  silver  cochineal"  in  the  trade;  but  that  obtained 
by  the  immersion  process,  and  known  as  "black 
cochineal,"  may  be  frequently  found  covered  with 
powdered  talcum,  calcium  sulphate,  lead  carbonate, 
and  even  stearin,  in  order  to  simulate  the  grayish 
color  of  the  "  silver  cochineal." 

Besides  the  above  impurities,  barium  sulphate, 
particles  of  lead,  vermilion,  chrome  red,  insects 
already  exhausted  of  their  coloring-matter,  and 
grains  of  substances  artificially  prepared  to  imitate 
the  dried  insect,  have  been  met  with  as  adulterants. 

The  pigment  upon  which  the  value  of  cochineal 
depends,  and  to  which  is  due  its  color,  was  first 
isolated  by  Pelletier  and  Caventou  in  1818,  and 
named  by  them  "  carmine."  This  was  found  to  be 
impure,  however,  and  it  was  only  in  1847  tnat 
Warren  de  la  Rue  succeeded  in  obtaining  the  pure 
pigment,  which  he  named  carminic  acid  (q.  v.). 

Properties:  Dried  cochineal  is  about  2  to  5  Mm. 
long,  nearly  hemispherical,  flat  or  slightly  concave 
beneath,  convex  above,  transversely  wrinkled,  pur- 
plish-gray or  purplish-black  in  color,  and  easily 
pulverizable,  yielding  a  dark-red  powder.  It  has  a 
faint,  heavy,  peculiar  odor,  and  a  slightly  bitterish, 
acidulous  taste,  and. swells  up  in  water,  to  which  it 
yields  its  coloring-matter,  which  is  soluble  also  in 
alcohol  and  in  ammonia,  slightly  soluble  in  ether, 
and  insoluble  in  fixed  and  volatile  oils. 

According    to     researches     by     Clark,    it    would 


COCHINEAL  51 

appear  that  the  coloring-matter,  carmine,  is  not 
present  in  the  living  insect  in  solution,  but  consists 
of  minute,  red  granules  surrounding  a  larger,  color- 
less granule  suspended  in  a  colorless  liquid. 

The  aqueous  infusion  of  cochineal  is  of  a  crimson- 
violet  color,  which  is  deepened  by  alkalies  and 
brightened  by  acids.  With  bismuth,  nickel,  and 
zinc  salts,  it  affords  lilac-colored  precipitates;  with 
iron  salts  a  dark-purple,  almost  black,  precipitate  is 
had ;  stannic  salts  give  a  brilliant  scarlet  and  stan- 
nous  salts  a  red  precipitate,  and  with  alum  it  forms 
lakes. 

Tests :  The  value  of  cochineal  as  an  indicator  de- 
pends on  its  carminic-acid  content.  The  process 
followed  by  Penny  for  testing  its  value  is  as  fol- 
lows:  i  Gm.  of  the  cochineal  is  digested  with  5 
Gm.  of  caustic  potassa  in  20  Cc.  of  distilled  water 
for  an  hour,  and  the  mixture  then  diluted  so  as  to 
measure  100  Cc.  Sufficient  of  a  i-per-cent.  potas- 
sium-ferricyanide  solution  is  then  added  to  10  Cc. 
of  the  mixture  to  convert  the  purple  into  a  yellow- 
ish-brown color.  The  quantity  required  for  this 
purpose  is  then  compared  with  that  required  for  a 
sample  of  cochineal  known  to  be  good. 

0.5  Cc.  of  a  i  :  80  aqueous  infusion  of  cochineal 
added  to  100  Cc.  of  distilled  water,  requires  3  Cc. 
of  centinormal  hydrochloric  acid,  and  2.8  Cc.  of 
centinormal  sodium  hydrate,  to  effect  changes  of 
color. 


52  INDICA 

Application :  Cochineal  is  an  exceedingly  valuable 
indicator.  It  is  used  in  the  form  of  solution  gen- 
erally, although  a  paper  is  also  prepared  (see  Test- 
Papers). 

A  cochineal  tincture  recommended  by  Luckow, 
and  which  is  very  sensitive,  is  made  by  macerating 
3  Gm.  of  whole  cochineal  in  250  Cc.  of.  a  mixture 
of  3  to  4  volumes  of  water  and  I  volume  of  alcohol, 
and  decanting  the  clear  solution.  The  whole  cochi- 
neal is  directed  to  be  used,  because  the  liquid  is 
difficult  to  filter  if  the  powdered  insect  is  used. 

The  color  of  these  solutions  is  a  deep,  ruby-red 
which  is  changed  to  a  violet  by  alkalies,  carbonates 
of  the  alkalies,  alkaline  earths,  sodium  phosphate, 
acetates  of  the  alkalies,  and  salts  of  the  weak  acids 
generally.  Acids  restore  the  red  color. 

Cochineal  is  very  serviceable  for  indicating  the 
carbonates  of  the  alkaline  earths  for  which  litmus  is 
inapplicable,  and  also  for  the  caustic  alkalies,  car- 
bonates and  sulphides.  Although  somewhat  influ- 
enced by  the  carbonic-acid  gas  or  hydrogen  sulphide 
liberated,  it  is  far  less  affected  by  these  than  is 
litmus.  It  is  also  particularly  useful  for  titrating  the 
ammonia  or  the  excess  of  sulphuric  acid  in  the  Kjel- 
dahl  nitrogen  estimation  process,  in  which  phenol- 
phtalein  is  not  very  serviceable. 

Cochineal  may  be  used  hot  or  cold  for  titrating 
carbonates  or  bicarbonates,  and  also  for  alkali  in 
soaps. 


COCHINEAL  53 

With  normal  sulphites  50$  of  the  base  may 
be  titrated  with  a  strong  acid.  For  organic  acids 
the  indicator  is  inapplicable.  With  phosphoric  acid, 
the  reaction  is  neutral  when  a  monobasic  salt  is 
formed,  as  acid  phosphates  are  neutral  to  cochineal. 

The  indicator  is  excellently  adapted  for  titrating 
the  alkaloids  generally,  and  morphine,  brucine,  atro- 
pine  and  cocaine  in  particular. 

On  account  of  the  acid  reaction  of  the  cochineal 
tincture  (or  carminic-acid  solution),  no  harm  is  done 
when  alkalies  are  being  titrated  with  acid.  When, 
however,  acids  are  being  titrated  with  alkalies,  the 
cochineal  tincture  must  be  first  neutralized  (colored 
violet  by  a  minute  quantity  of  ammonia);  the  end 
of  the  reaction  is  then  indicated  by  the  violet  color. 

Tincture  of  cochineal  is  best  kept  in  an  acid  con- 
dition, because  the  neutral  or  alkaline  tincture  soon 
spoils.  In  use,  the  absence  of  iron,  aluminum,  or 
copper  salts  must  be  assured  from  the  solutions  to 
be  operated  on,  as  these  salts  yield  a  pink  color, 
even  when  solutions  are  acid.  The  tincture  is  also 
particularly  serviceable  for  titrations  by  artificial 
light,  as  the  change  of  color  is  very  sharply  defined, 
and  the  depth  of  the  colors  enhanced.  The  sodium 
flame  is  very  useful  with  this  indicator. 


54  INDICA  TCRS 

COLEIN 

C,oH100. 

ALKALIES  =  Yellow  ACIDS  =Red 

Source  :  Colein  is  a  resin-like  substance  isolated 
from  the  stems  and  leaves  of  Coleus  verschaffelti. 
It  was  first  obtained  and  described  by  A.  H. 
Church  in  1877. 

Preparation  :  Colein  is  obtained  by  crushing  the 
stems  and  leaves  of  Coleus  verschaffelti  with  a  small 
quantity  of  alcohol  faintly  acidulated  with  sulphuric 
acid,  expressing  the  crimson  pulp  (avoiding  contact 
Nvith  metals),  shaking  the  liquid  obtained  with  ba- 
rium carbonate,  and  filtering.  Most  of  the  alcohol  is 
then  distilled  off,  and  at  a  certain  stage  a  deep- 
colored,  resin-like  substance  sinks  to  the  bottom  of 
the  vessel  beneath  a  supernatant  rich-red  liquid. 
The  precipitated  matter  is  the  colein,  and  it  is  puri- 
fied by  dissolving  it  in  alcohol  and  reprecipitating  it 
by  the  addition  of  ether  or  water  ;  the  purifying 
process  is  repeated  several  times. 

Properties  :  Pure  colein  is  a  brittle,  resinous  sub- 
stance, having  aconchoidal  fracture,  and  yielding  a 
reddish-purple  powder  verging  on  crimson.  It  is 
freely  soluble  in  alcohol,  very  difficultly  so  in  water, 
and  insoluble  in  ether.  It  yields  red  solutions,  but 
the  alcoholic  solution  soon  loses  its  color,  owing, 
probably,  to  union  with  a  portion  of  alcohol.  The 


COA'CO   RED  SS 

color  may,  however,  be  restored  by  the  addition  of 
a  drop  of  sulphuric  acid.  Concentrated  sulphuric 
acid  dissolves  it  unchanged,  but  nitric  acid  con- 
verts it  into  a  brown,  resinous  mass.  Concentrated 
caustic  alkalies  (even  ammonia)  profoundly  alter  it. 
Its  composition,  from  analyses  made  by  Church,  is 
C,0H100,. 

Application  :     Boettger   recommended   colein    as    an 
indicator,  but  it  has  found  very  little  use,  so  far. 

Colein  Test-Paper  is  also  used  (see  under  Test- 
Papers). 


CONGO   RED 

(C6H4)9.(Na)i.(CioHa)9.(NH,.SO,Na)9 

ALKALIES  =  Red  ACIDS  =  Blue 

Synonyms:  Sodium  Tetrazodiphenyl-naphtionate; 
Sodium  Diphenyl-diazobinaphtionate. 

Preparation:  Congo  red  was  discovered  by  Boettger 
in  1884.  It  is  the  sodium  salt  of  diphenyl-diazo- 
binaphtionic  acid,  and  is  obtained  by  dissolving 
28.2  parts  of  benzidine  sulphonate  in  500  parts  of 
water,  adding  first  30  parts  of  hydrochloric  acid 
(20°  Be.),  and  then  13  parts  of  sodium  nitrite  dis- 
solved in  50  parts  of  water,  in  small  portions. 
The  solution  is  cooled,  and  to  it  is  then  added  a 
solution  of  55  parts  of  sodium  naphtionate  and  12 
parts  of  sodium  acetate  in  100  parts  of  water. 


$6  INDICA  TOXS 

The  precipitate  is  collected,  dissolved  in  a  solution 
of  sodium  carbonate,  and  the  dye  salted  out,  and 
dried. 

Properties:  Congo  red  occurs  as  reddish-brown 
lumps  which  are  readily  soluble  in  water  and  in 
alcohol.  Its  solutions  are  very  sensitive  to  free 
acids,  which  yield  a  blue  color  and  liberate  the 
base ;  alkalies  restore  the  red  color. 

Application :  Congo  red  is  very  useful  for  estimating 
free  acids,  more  particularly  as  acid  salts  do  not 
affect  it.  It  may,  therefore,  be  employed  for  esti- 
mating sulphuric  acid  in  aluminum  sulphate,  as  the 
alum  has  no  action  on  it.  Free  carbonic  or  acetic 
acid,  present  to  the  extent  of  only  0.002^,  suffices 
to  yield  the  blue  color.  But,  if  a  drop  of  ammonia 
water  is  added  to  the  solution,  a  stream  of  car- 
bonic-acid gas  may  be  passed  through  it  without 
the  blue  color  being  produced.  Hydrogen  sulphide 
also  yields  the  blue  color;  nor  does  boiling,  the 
solution  remedy  the  change  effected  by  the  hydro- 
gen sulphide  or  carbonic-acid  gas. 

Congo  red  may  be  used  for  estimating  mineral 
acids  in  the  presence  of  organic  acids,  as  the  latter 
do  not  affect  it. 

Congo  red  is  also  useful  for  titrating  aniline  and 
toluidine  in  the  residual  liquors  from  aniline -works. 
For  this  purpose,  the  liquid  is  diluted  with  water 
until  a  perfect  solution  is  had,  then  an  alcoholic 


CONGO   RED  57 

Congo-red  solution  is  added,  and  finally  sufficient 
sulphuric  or  hydrochloric  acid  carefully  added  until 
a  decided  bluish-violet  color  is  observed  (a  distinct 
blue  is  seen  only  when  a  decided  excess  of  acid  is 
added). 

Sulphates,  chlorides,  and  nitrates  of  the  alkalies 
seriously  interfere  with  the  end-reaction,  hence 
their  absence  should  be  assured. 

Bisulphites  and  biphosphates  are  neutral  to  Congo 
red.  For  organic  acids  the  indicator  is  useless. 

Phosphates  may  be  titrated  by  means  of  Congo 
red ;  sulphites,  however,  cannot ;  and  bichromates 
are  neutral  to  the  indicator,  whereas  the  chromates 
are  alkaline. 

Congo-red  solution  for  titrimetric  use  is  made  by 
dissolving  I  part  of  Congo  red  in  100  parts  of  30- 
per-cent.  alcohol,  about  10  drops  being  added  to 
100  Cc.  of  the  liquid  to  be  titrated.  The  sensitive- 
ness of  the  solution  is  such  that  o.  I  Cc.  added  to 
IOO  Cc.  of  distilled  water  requires  only  0.7  Cc. 
of  centinormal  hydrochloric  acid,  and  O.6  Cc.  of 
centinormal  ammonia,  to  produce  the  changes  of 
color,  but  requires  2.5  Cc.  of  centinormal  potassa. 

Congo  paper  is  also  used  as  an  indicator,  and  is 
treated  of  under  Test-Papers.  ^ 


58  INDICA  TORS 

CORALLIN 

C)8HI403 

ALKALIES  =  Violet-red  ACIDS  =  Yellow 

Synonyms:   Aurine;   Commercial  Rosolic  Acid. 

Preparation  and  Properties:   See  Rosolic  Acid. 

Application:  Corallin'  test  solution  may  be  prepared 
by  dissolving  I  Gm.  of  Corallin  in  10  Cc.  of  alco- 
hol, and  adding  distilled  water  to  make  up  to  100 
Cc.  The  solution  is  colored  violet-red  by  alkalies, 
and  yellow  by  acids.  It  is  especially  useful  for 
titrating  free  ammonia. 

CORALLIN   RED 

C19HJ30,.NH, 

ALKALIES  =  Red  ACIDS  =  Yellow 

Synonyms:  Paeonin;  Aurine  R.  ;  Impure  Rosani- 
line  Rosolate;  Diamidotriphenylcarbidride. 

Preparation:  Corallin  red  was  discovered  by  Marnas. 
It  is  obtained  by  heating  one  part  of  commercial 
rosolic  acid  (corallin ;  aurine)  with  three  parts  of 
ammonia  in  a  closed  vessel  at  a  temperature  of 
140°  C.  The  semi-liquid  mass  is  then  treated  with 
hydrochloric  acid,  and  the  precipitate  collected, 
washed,  and  finally  dried. 

Corallin    red  is   believed  to  be  most  probably  a 
product     intermediate    between     aurine    and    para- 


CURCUMIN  59 

rosaniline,  in  which  the  hydroxyl  is  replaced  by  an 
amido  group. 

Properties:  Corallin  red  occurs  as  a  reddish-brown 
powder,  which  is  readily  soluble  in  alcohol,  insol- 
uble in  cold  water,  and  but  slightly  soluble  in  boil- 
ing water.  Its  solutions  have  a  beautiful  red  color, 
which  is  changed,  even  by  a  trace  of  acid,  to  a 
yellow. 

The  formula  assigned  to  it  is  C19H13O2(NH,). 

Application :  Like  Commercial  Rosolic  Acid  (which 
see). 

CURCUMIN 

ALKALIES  =  Reddish-brown  ACIDS  =  Yellow 

Synonyms:  Turmeric  Yellow;   Curcummin. 

Source :  Curcumin  is  a  coloring-matter  obtained 
from  the  roots  of  Curcuma  longa  L.,  one  of  the 
Zingiberaceae,  and  found  in  the  East  Indies,  China, 
and  Madagascar.  It  was  first  isolated  by  Vogel, 
who  also  found  in  the  root  another,  a  brown  col- 
oring-matter. 

Preparation  :  Curcumin  is  obtained  by  first  exhaust- 
ing curcuma  roots  with  water  to  remove  the  brown 
matter,  extractive,  etc.,  then  drying,  powdering, 
and  exhausting  with  alcohol,  which  takes  up  the 
curcumin.  The  alcohol  is  next  distilled  off,  the 
dried  residue  treated  with  ether,  and  the  filtered 


60  INDICA  TORS 

ethereal  solution  evaporated.  The  impure  cur- 
cumin  so  obtained  is  dissolved  in  alcohol,  precip- 
itated by  lead  acetate,  the  precipitate  collected 
and  washed  with  alcohol,  and  decomposed  by  a 
current  of  hydrogen  sulphide  while  suspended  in 
water.  This  precipitate  is  then  collected,  dried, 
and  exhausted  with  ether  which,  on  evaporation, 
deposits  pure  curcumin. 

Gajewski,  in  1870,  obtained  pure  curcumin  by 
removing  the  fatty  matter  from  the  root  with  carbon 
disulphide,  then  extracting  the  coloring-matter  with 
ether,  and  recrystallizing  from  ether  or  hot  ben- 
zene. In  1873  he  modified  the  process  by  washing 
the  ethereal  extract  with  weak  ammonia,  and  pre- 
cipitating the  pure  curcumin  by  means  of  a  current 
of  carbonic-acid  gas. 

Daube  also,  in  1870,  obtained  the  curcumin  by 
exhausting  the  roots  with  boiling  benzene,  and  dis- 
solving the  crystals  obtained  on  cooling,  in  cold 
alcohol,  precipitating  the  filtrate  with  alcoholic 
lead-acetate  solution,  decomposing  the  precipitate 
with  hydrogen  sulphide,  and  crystallizing  from 
alcohol. 

The   yield   of   curcumin    is   about   0.3    per   cent. 

Properties:  Curcumin  occurs  as  a  cinnamon-colored, 
translucent,  foliaceous  mass  which  yields  a  yellow 
powder  melting  at  40°  C.,  or  as  yellow  prisms  or 
crystalline  powder  melting  at  178°  C.  (183°  C.  Cia- 
mician  and  Silber). 


CURCUMIN  6 1 

Curcumin  is  insoluble  in  water,  is  somewhat  sol- 
uble in  hot  benzene,  and  is  readily  soluble  in  ether, 
alcohol,  acetic  acid,  alkalies,  fats,  and  in  oils.  On 
exposure  to  sunlight  it  is  bleached. 

Curcumin  yields  with  alkalies  intensely  reddish- 
brown  solutions ;  and  similar  solutions  are  afforded 
by  the  alkaline  earths  and  borax.  Acids  restore 
the  yellow  color.  In  concentrated  sulphuric  acid, 
curcumin  dissolves  with  a  carmine  color;  in  phos- 
phoric and  in  hydrochloric  acids  it  dissolves  with- 
out decomposition,  and  also  with  a  carmine  color. 
Nitric  acid  decomposes  it. 

Boric  acid  added  to  an  alcoholic  solution  of  cur- 
cumin does  not  change  the  color  of  the  latter,  but 
on  boiling  and  evaporating,  a  carmine-red  residue 
remains.  This  compound  is  decomposed,  accord- 
ing to  Schlumberger,  by  long  contact  with  water, 
yielding  a  resinous  yellow  substance,  known  as 
pseudo-curcumin,  which  does  not  yield  a  red  color 
with  boric  or  hydrochloric  acid,  and  dissolves  in 
alkalies  with  a  greenish-gray  color. 

The  curcumin-boric-acid  compound  yields  with 
alkalies,  reddish-violet  solutions  which  rapidly 
become  gray.  On  boiling  an  alcoholic  solution  of 
the  compound  with  sulphuric  acid,  a  dark,  blood- 
red  color  develops,  and  on  cooling,  rosocyanine 
deposits. 

Curcumin  solutions  exhibit  a  green  fluorescence, 
and  yield  brown,  insoluble  lakes  with  lead,  lime, 
and  baryta. 


62  INDICA  TOR '3 

Application  :  The  sensitiveness  of  curcumin  appears 
to  be  increased  by  the  presence  of  most  salts,  hence 
the  indicator  is  applicable  to  a  wide  variety  of 
titrimetric  determinations.  It  is  also  applicable  in 
the  presence  of  ammonia,  to  which  it  is  insensitive. 
It  is  sensitive,  however,  to  carbonic  acid,  and  is 
acid  to  bicarbonates  of  the  alkalies. 

With  the  sulphates  and  sulphides  of  the  alkalies, 
the  indicator  shows  when  half  of  the  combined 
alkali  becomes  a  sulphate  or  sulphide;  i.e.,  when 
bisulphates  or  bisulphides  are  formed.  With  sul- 
phites and  phosphates  the  end-reaction  is  not  def- 
inite; hence,  for  these  the  indicator  is  useless.  In 
sodium  silicate  only  90$  of  the  sodium,  and  in 
borax  only  50$  of  the  sodium,  is  shown,  and  the 
end-reaction  is  uncertain. 

Sodium  thiosulphate  is  neutral  to  the  indicator. 


CURCUMIN   W. 

CH3.(CaH,.SO3Na.N),O 

ALKALIES  =  Red  ACIDS  =  Greenish  Yellow 

Synonyms'  Curcumin  S.  ;  Sun  Yellow;  Sodium  (or 
Ammonium)  Azoxystilbene-disulphonate. 

Preparation:  Curcumin  W.  is  obtained  by  dissolving 
5  parts  of  sodium  (or  ammonium)  para-nitrotolu- 
enesulphonate  in  70  parts  of  water,  adding  3  parts 
of  soda-lye  (40°  Be\),  and  warming  the  mixture 


CYANINE  63 

while  stirring  vigorously.  When  the  color  has 
changed  from  a  saffron  to  a  yellowish-red  the  dye 
is  salted  out  and  dried. 

Properties :  Curcumin  W.  forms  a  reddish-brown 
powder,  soluble  in  water,  and  yielding  a  yellow 
solution,  the  color  of  which  is  changed  to  a  red  by 
alkalies,  and  restored  by  acids. 

Application :  Curcumin  W.  was  recommended  by 
Storch,  who  states  that  it  is  more  sensitive  than 
phenolphtalein.  Salts  which  ordinarily  affect  the 
sensitiveness  of  indicators  appear  to  even  increase 
that  of  Curcumin  W.  It  is  neutral  to  bicarbonates, 
and  is  serviceable  for  ammonia.  Carbonic-acid  gas 
affects  it.  The  indicator  may  be  used  in  those 
cases  where  other  indicators,  such  as  phenolphta- 
lein and  curcuma,  cannot  be  used  for  ammonia. 

CYANINE 

CeH5.CH2.C9HflN.C.C9HaNCl. 

ALKALIES  =  Deep  Blue  ACIDS  =  Colorless 

Synonyms:  Quinoline  Blue;    Diamylcyanine  Iodide. 

Preparation  :  Cyanine  was  discovered  by  Greville 
Williams  in  1856.  It  is  prepared  by  heating  a 
mixture  of  equivalent  quantities  of  quinoline  and 
lepidine  (^-methylquinoline)  with  amyl  iodide, 
then  heating  the  resulting  product  with  potassa, 
and  finally  crystallizing. 


C>4  INDICA  TORS 

Properties  :  Cyanine  is  obtained  in  the  form  of  shin- 
ing prisms  or  plates  having  a  green  metallic  luster. 
The  crystals  are  insoluble  in  cold  water,  difficultly 
soluble  in  boiling  water,  with  which  they  yield  a 
violet-blue  solution  having  a  quinoline  odor,  and 
are  soluble  in  alcohol  with  deep,  blue  color.  Acids 
discharge  the  color,  which  is  restored  by  alkalies. 
Cyanine  dissolves  in  concentrated  sulphuric  acid, 
and  the  colorless  solution,  on  heating,  yields  iodine 
vapors. 

Application  :  Cyanine  is  very  sensitive  to  acids,  even 
carbon  dioxide  sufficing  to  discharge  the  color.  It 
is  capable  of  but  limited  use,  however. 


DIAZO-PARANITRANILINE-GUAIACOL 

NOaC9H4N:NC6H3(OCH3)OH 

ALKALIES  =  Red  ACIDS  =  Greenish-yellow 

Synonym:      Riegler's  Indicator. 

Preparation  :  The  indicator  is  prepared  by  adding  a 
solution  of  diazo-paranitraniline  to  an  alkaline  solu- 
tion of  guaiacol. 

Properties:  Diazo-paranitraniline  forms  a  brown 
substance  insoluble  in  water  but  soluble  in  alcohol. 
Its  composition  is  represented  by  the  formula 
NO3C6H4N  :  NC8H3(OCH3)OH. 


D IME  TH  YLA  MID  OA  ZOBENZENE  6  5 

Application  :  This  indicator  has  but  very  recently 
been  introduced  by  E.  Riegler,  who  states  that  a 
solution  of  0.2  Gm.  in  100  Cc.  of  alcohol  is  much 
more  sensitive  than  phenolphtalein.  One  or  two 
drops  of  the  solution  added  to  an  alkaline  solution 
suffice  to  color  the  latter  a  very  handsome  red, 
changed  by  an  excess  of  acid  to  a  greenish-yellow 
color. 


DIMETHYLAMIDOAZOBENZENE 

C8H5.Na:C6H4N(CH3)!, 

ALKALIES  —  Yellow  ACIDS  —  Red 

Synonyms:  Butter  Yellow;  Aniline-azodimethyl- 
aniline ;  Benzene-azodimethylaniline. 

Preparation  :  Dimethylamidoazobenzene  was  dis- 
covered in  1875  by  O.  N.  Witt.  The  indicator  is 
prepared  by  dissolving  9.3  Gm.  of  aniline  in  30  Gm. 
of  a  25-per-cent.  hydrochloric  acid,  and  after  cool- 
ing the  solution  and  diluting  it,  adding  7  Gm.  of 
sodium  nitrite  previously  dissolved  in  water,  where- 
by the  aniline  hydrochloride  is  converted  into  diazo- 
benzene  chloride.  The  mixture  is  now  stirred  well, 
and  poured  into  a  solution  of  12  Gm.  of  dimethyl- 
aniline  in  15  Gm.  of  hydrochloric  acid,  30  Gm.  of 
sodium  acetate  being  then  added.  The  crystals, 
which  soon  separate,  are  then  recrystallized  from 
alcohol. 


66  2ND  1C  A  TORS 

Properties  :  Dimethylamidoazobenzene  crystallizes 
in  the  form  of  golden-yellow  scales  which  melt  at 
115°  C.,  and  are  soluble  in  alcohol,  strong  mineral 
acids,  alkaline  solutions  and  oils,  but  insoluble  in 
water.  In  dilute  solutions  of  dimethylamidoazo- 
benzene,  even  traces  of  acids  yield  a  handsome  red 
color,  which  is  changed  to  yellow  by  alkalies. 

Application  :  Dimethylamidoazobenzene  was  recom- 
mended by  B.  Fischer  and  O.  Phillip  as  an  indica- 
tor instead  of  methyl  orange,  because  the  transition 
from  the  lemon-yellow  to  red  is  more  easily  ob- 
served than  the  change  from  orange  to  red  exhib- 
ited by  methyl  orange,  and  also  because  the  indi- 
cator may  be  readily  prepared  by  the  operator, 
whereby  a  constant  and  definite  preparation  may 
always  be  at  command  (which  is  not  the  case  with 
methyl  orange). 

Lunge  and  Thompson  state,  however,  that  methyl 
orange  is  more  sensitive  than  the  dimethylamido- 
azobenzene,  and  that,  in  equal  concentration,  it 
will  exhibit  similar  shades  of  color. 

For  use,  a  1:200  alcoholic  solution  of  dimethyl- 
amidoazobenzene  is  made,  about  5  drops  being 
added  to  100  Cc.  of  the  liquid  to  be  titrated.  The 
color  of  the  liquid  will  be  lemon  yellow,  and 
changed  sharply  by  acids  to  a  handsome  carnation 
red.  Carbonic-acid  gas  does  not  affect  the  indicator. 


DIPHENYLAMINE 


DIPHENYLAMINE 

(C,H6)2NH 

Synonym :    Phenylaniline. 

Preparation:  Diphenylamine  is  obtained  by  the 
dry  distillation  'of  triphenyl-rosaniline  (aniline  blue), 
and  by  heating  aniline  hydrochloride  with  aniline  to 
240°  C. 

Properties:  Diphenylamine  occurs  as  a  grayish, 
crystalline  mass,  or  white  crystals,  slightly  soluble 
in  water,  easily  soluble  in  alcohol  and  in  ether,  and 
fairly  so  in  acids,  with  which  it  forms  salts.  It  is  a 
very  weak  base,  however,  its  salts  being  decomposed 
even  by  water.  It  has  a  pleasant  odor,  melts  at 
54°  C.,  and  boils  at  310°  C.  A  i-per-cent.  solu- 
tion in  concentrated  sulphuric  acid,  forming  diphe- 
nyl-sulphonic  acid,  is  colored  intensely  blue  by 
nitric  acid.  It  is  also  temporarily  colored  by 
nitrous  acid,  the  color  gradually  fading  to  a  green- 
ish yellow;  hypochlorous,  permanganic,  molybdic, 
and  selenous  acids  likewise  color  it  somewhat;  and 
so  do  certain  ferric  salts,  barium  salts,  and  hydrogen 
dioxide.  Ozone  colors  the  alcoholic  solution,  or 
test-paper  prepared  from  the  latter,  a  yellow  to 
brown. 

Application  :  According  to  Longi,  diphenylamine  is 
serviceable  as  an  indicator  in  the  volumetric  deter- 


68  2ND  1C  A  TORS 

mination  of  nitric  acid  using  a  decinormal  solution 
of  stannous  potassium  sulphate. 

Diphenylamine  is  principally  employed  for  the 
detection  of  nitrates  in  potable  water,  or  in  wine  or 
milk  to  which  any  water  containing  nitrates  has  been 
added.  Traces  of  nitric  acid  in  sulphuric  acid  may 
also  be  detected  by  means  of  it. 

In  testing  water,  wine,  or  milk,  a  few  drops  of 
diphenylamine  solution  are  added  to  I  Cc.  of  the 
liquid,  and  then  I  Cc.  of  concentrated  sulphuric 
acid  is  added  so  as  to  form  a  lower  layer.  At  the 
zone  of  contact  a  blue  color  develops,  and  is  so  in- 
tense that  I  part  of  nitric  acid  in  3,000,000  parts  of 
liquid  is  readily  detected. 

EOSINE 

CaH4.(CO)2.O.(C6HBra.NaO)a 
ALKALIES  =  Green  Fluorescence         ACIDS  =  Yellow 

Synonyms:  Eosine  Yellowish;  Bromeosine;  Tetra- 
bromeosine;  Tetrabromfluoresceine ;  Tetrabromo- 
resorcinphtalein. 

Preparation  :  Eosine  was  discovered  in  1874  by 
Caro.  It  may  be  obtained  by  the  action  of  bromine 
on  fluoresceine,  C6H4.CO,.C.O.(C6H,)2(OH)2,  in  a 
cold  solution  in  glacial  acetic  acid,  some  potassium 
chlorate  being  finally  added  to  the  mixture  in  order 
to  decompose  the  hydrobromic  acid  formed,  where- 
by a  saving  is  effected  in  the  quantity  of  bromine 


EOSINE  69 

required.  Four  hydrogen  atoms  of  the  fluoresceine 
are  thus  replaced  by  an  equal  number  of  bromine 
atoms,  and  the  tetrabrorhfluoresceine  gradually 
separates  in  the  form  of  yellowish-red  crystals, 
which  are  purified  by  recrystallization  from  alcohol, 
and  finally  converted  into  a  potassium  or  sodium 
salt,  which  is  the  commercial  form  of  the  article. 

Eosine  is  also  obtained  by  heating  in  an  enam- 
elled steam-kettle  a  solution  of  120  parts  of  soda 
lye  (36°  Be".)' and  300  parts  of  water,  and  gradually 
adding  64  parts  of  bromine.  There  results  from 
the  reaction  sodium  bromide,  sodium  bromate,  and 
sodium  hypobromite.  The  mixture  is  then  heated 
for  half  an  hour  to  convert  the  last  into  bromate. 
The  solution  is  then  cooled,  and  to  it  is  added  a 
cooled  solution  of  32  parts  of  fluoresceine,  300 
parts  of  water,  and  50  parts  of  soda  lye  (36°  Be.). 
The  mixture  is  briskly  stirred,  and  280  parts  of 
hydrochloric  acid  gradually  added,  the  whole  boiled 
for  5  minutes  and  600  parts  of  cold  water  added. 
The  precipitate  is  then  collected  and  dried.  The 
boiling  and  addition  of  water  are  usually  repeated 
once  or  twice  to  remove  all  traces  of  hydrochloric 
acid.  The  dye  is  then  converted  into  a  potassium 
or  sodium  salt. 

Properties  :  Uncombined  cosine  occurs  as  yellowish- 
red  crystals  containing  some  alcohol  of  crystalliza- 
tion. It  is  almost  insoluble  in  water,  but  yields 
readily  soluble,  bibasic  salts  with  alkalies. 


7O  fNDICA  TORS 

The  potassium  salt  of  cosine  forms  bluish-red 
crystals,  or  a  brownish  powder.  It  is  soluble  in 
water  and  in  alcohol,  and  yields  solutions  having  a 
magnificent  green  fluorescence.  Acids  destroy  the 
fluorescence,  the  solution  becoming  yellow.  Mineral 
acids  cause  a  yellowish-red  precipitate  in  the  solu- 
.tions.  Organic  acids  only  partially  decompose  the 
salt.  Eosine  yields  handsome,  insoluble  lakes  with 
salts  of  lead  and  tin,  and  with  alumina. 

Application  :  Eosine  is  peculiarly  applicable  for  use 
in  dark-colored  solutions,  in  which  the  ordinary 
color-changes  can  be  observed  only  with  difficulty 
or  not  at  all.  It  is  also  useful  for  the  titration  of 
soap,  and  for  alkalies. 

For  use  as  an  indicator  a  3-per  cent,  aqueous 
solution  is  prepared,  of  which  about  10  drops  are 
added  to  100  Cc.  of  the  liquid  to  be  titrated. 

EOSINE-METHYLENE    BLUE 

ALKALIES  =  Red  ACIDS  =  Blue 

Preparation  :  The  compound  is  prepared  by  mixing 
stoichiometrical  equivalents  of  basic  cosine  and 
methylene  blue  dissolved  in  alcohol. 

Properties  :  The  alcoholic  solution  of  the  compound 
has  a  bluish-violet  color  which  is  changed  by  organic 
and  other  acids,  as  well  as  acid  compounds,  to  a 
pure  blue  or  bluish-green  ;  and  by  alkalies,  and 


ETHYL   ORANGE  J I 

alkaline  substances,  to  a  red  color.  The  neutrality 
point  is  always  indicated  by  the  restoration  of  the 
original  bluish-violet. 

Application :  Eosine-methylene  blue  is  said  by 
H.  Rosin  to  be  exceedingly  sensitive — so  much  so 
that  glass,  which  is  alkaline  in  spots,  is  colored  red 
in  those  places  by  the  solution.  The  solution  is 
also  applicable  as  a  sensitive  biochemical  reagent,  as 
it  affords  characteristic  colors  with  pathological 
elements. 

ETHYL  ORANGE 

C6H4.SO3Na.Na.C8H4N(C2H6)9 

ALKALIES  =  Yellow  ACIDS  =  Red 

Synonyms:  Diethylaniline  Orange;  Sodium  (or 
Ammonium)  Diethylamidoazobenzene-sulphonate ; 
Sodium  (or  Ammonium)  Diethylaniline-azoben- 
zene-sulphonate. 

Preparation :  Ethyl  orange  is  prepared  in  exactly 
the  same  manner  as  methyl  orange  (which  see), 
diethylaniline  being  substituted  for  the  dimethyl- 
aniline  in  the  formula. 

Properties:  Ethyl  aniline  occurs  as  an  orange-yellow 
crystalline  powder,  soluble  in  alcohol,  and  almost 
insoluble  in  water. 

Application:  Ethyl  orange  has  been  recommended 
as  being  more  delicate  than  methyl  orange.  It  L 


72  1NDICA  TORS 

sensitive  to  free  acids,  and  is  colored  red  even  by 
neutral  aluminum  sulphate.  It  may  be  used  like 
methyl  orange,  but  is  not,  however,  as  sensitive  as 
the  latter. 

A  solution  of  I  part  in  400  parts  of  3<D-per-cent.- 
alcohol  is  used,  3  to  5  drops  of  which  are  added  to 
100  Cc.  of  the  solution  to  be  titrated.  Its  sensi- 
tiveness is  such  that  100  Cc.  of  distilled  water  to 
which  0.2  Cc.  of  the  indicator-solution  has  been 
added  will  require  3  Cc.  of  decinormal  hydrochloric 
acid  (methyl  orange  similarly  tested  requires  only 
I  Cc.  of  centinormal  acid). 


EUPITTONIC   ACID 


ALKALIES  —  Blue  ACIDS  =  Carmine  Red 

Synonyms  :  Eupitton  ;  Pittakal  ;  Hexaoxymethyl- 
aurin  ;  Hoffmann's  Indicator. 

Preparation  :  Eupittonic  acid  was  first  isolated  by 
Liebermann  from  pittakal,  which  was  discovered  in 
1835  by  Reichenbach  during  the  fractional  distilla- 
tion of  beech-tar  creosote  on  treating  certain  por- 
tions of  the  distillates  with  baryta  and  exposing  to 
air.  Later  on  Hoffmann  demonstrated  'that  the 
pittakal  resulted  from  the  oxidation  of  pyrogallol- 
dimethyl  ether  and  the  dimethyl  ether  of  methyl- 
pyrogallol,  the  reaction  occurring  as  follows  : 


EUPITTONIC  ACID  73 

C8fro(OCH8),OH  +  C.Ha(CH3).(OCH8),OH  +  3O 

pyrogallolmethyl  ether  methylpyrogallol-dimethyl  ether 

=  Cl.H.(OCH,).0,  +  3H10 

eupittonic  acid 

Eupittonic  acid  is  prepared  by  dissolving  2  mo- 
lecular weights  of  pyrogalloldimethyl  ether  and  I 
molecular  weight  of  methylpyrogalloldimethyl 
ether  in  alcohol,  adding  an  excess  of  caustic  soda, 
and  heating  the  mixture  on  an  oil-bath  for  half  an 
hour  to  a  temperature  of  from  200°  to  220°  C. 
The  mass  soon  becomes  greenish,  then  blue.  It  is 
then  treated  with  hydrochloric  acid,  and  the  brown- 
ish-red residue  crystallized  by  dissolving  in  alcohol 
and  precipitating  with  ether. 

Properties  •  Eupittonic  acid  occurs  as  orange-yellow 
crystals, .insoluble  in  water,  soluble  in  alcohol  and 
in  ether,  and  yielding  with  glacial  acetic  acid  a 
brown  solution.  The  acid  is  bibasic,  and  yields 
with  alkalies  blue  compounds  soluble  in  water,  with 
a  violet-blue  color.  The  solutions  are,  however, 
precipitated  by  an  excess  of  alkali.  In  ammoniacal 
solutions  it  dissolves  with  a  reddish-blue  color. 
Acids  change  the  color  of  alkaline  solutions  to  a 
carmine-red.  With  salts  of  lead,  tin,  and  other 
heavy  metals  eupittonic  acid  yields  blue,  difficultly 
soluble  lakes. 

Application :  Eupittonic  acid  is  practically  unused  as 
an  indicator.  Its  sensitiveness  is  stated  to  be  such, 
however,  that  0.6  Cc.  of  centinormal  alkali  suffices 


74  INDICA  TORS 

to  afford  a  distinct  change  in  50  Cc.  of  solution  con- 
taining the  indicator. 


FLAVESCIN 
ALKALIES  =  Intense  Yellow  ACIDS  =  Colorless 

Synonym :    Lux's  Indicator. 

Source '.  Flavescin  is  a  peculiar  coloring-matter  ob- 
tained from  oak  shavings. 

Preparation:  It  is  obtained  by  passing  hot  air  satu- 
rated with  steam  through  oak  shavings,  condensing 
the  vapors  in  a  cooled  receiver,  filtering  the  liquid 
thus  obtained,  and  shaking  it  out  two  or  three 
times  with  ether.  The  ethereal  solution,  contain- 
ing the  flavescin  and  empyreumatic  acids,  is  evap- 
orated, and  the  vessel  heated  to  40°  or  50°  C., 
while  a  current  of  air  is  passed  through  it  until  the 
odor  of  acetic  acid  has  disappeared.  The  brown- 
ish residue  is  then  digested  with  ten  or  twenty 
volumes  of  cold  water;  this  treatment  yields  a  con- 
centrated solution  of  flavescin,  which  is  preserved 
by  diluting  it  with  several  volumes  of  alcohol. 

Properties  :  Flavescin  occurs  as  a  brown,  translucent, 
tenaceous  mass,  readily  soluble  in  water,  alcohol,  and 
in  ether.  It  yields  colorless  solutions  changed  to  an 
intense  yellow  by  alkalies.  The  reaction  is  very 
sharp,  and  is  clearly  seen  even  by  artificial  light. 
Nascent  carbonic-acid  gas  and  bicarbonates  de- 


FL  UORES  CEIN  7  5 

colorize  it,  the  coloration  and  decoloration  being 
more  rapid  in  alcoholic  solution.  Flavescin  is 
decomposed  by  most  inorganic  and  organic  acids, 
the  solution  being  decolorized.  Even  the  fatty- 
and  resin-acids  act  thus.  The  color  is,  however, 
restored  by  alkalies. 

Application :  Flavescin  was  recommended  by  Warder 
F.  Lux  as  an  indicator,  and  in  his  hands  has  given 
results  closely  agreeing  with  those  of  other  indi- 
cators. It  is  not  serviceable,  however,  for  titrating 
small  quantities  of  caustic  alkalies  when  consider- 
able quantities  of  carbonates  of  the  alkalies  are 
present,  although  it  is  useful  for  carbonates  in  the 
presence  of  bicarbonates,  and  also  for  carbonic  acid. 
The  reaction  occurring  with  carbonates  is  due  to  the 
decomposition  of  the  latter  into  a  bicarbonate  and 
a  compound  of  flavescin.  It  is  useful  for  inorganic 
acids,  as  well  as  for  organic  acids. 

FLUORESCEIN 

(C8H3OH)2.C.O.(C6H4.COO) 

Green  No 

ALKALIES  =  „  ACIDS  = 

Fluorescence  Fluorescence 

Synonyms :  Resorcin-phtalein  ;  Diresorcin-phtalein  ; 
Tetra-oxyphtalophenone ;  Uranine;  Kruger's  In- 
dicator. 

Preparation :  Fluorescein  was  discovered  by  Baeyer 
in  1871.  It  is  prepared  by  heating  an  intimate 


7  2ND  1C  A  TORS 

mixture  of  2  molecular  weights  of  resorcin  and 
I  molecular  weight  of  phtalic  anhydride  on  an 
oil-bath  at  a  temperature  of  from  190°  to  200°  C., 
until  aqueous  vapors  are  no  longer  evolved.  It  is 
important  that  pure  materials,  particularly  resorcin, 
be  used,  in  order  to  obtain  a  pure  product.  If 
impure  materials  are  employed,  the  final  purifi- 
cation of  the  fluorescein  is  rendered  extremely 
difficult. 

The  mass  obtained  is  then  treated  with  boiling 
water,  and  the  residue  is  powdered,  dissolved  in 
potassa  solution,  and  reprecipitated  by  means  of 
an  acid. 

Tests  :  The  flubrescence  of  a  solution  of  o.  I  Cc.  of 
a  1:100  fluorescein-solution  in  100  Cc.  of  distilled 
water  is  destroyed  by  th^  addition  of  0.5  Cc.  of 
decinormal  hydrochloric  acid. 

Properties:  Pure  fluorescein  occurs  as  a  yellowish- 
red,  crystalline  powder,  or  dark-brown  crystals,  in- 
soluble in  water.  It  is  but  difficultly  soluble  in 
cold  alcohol,  more  readily  soluble  in  boiling 
alcohol,  and  quite  soluble  in  ether  and  in  dilute 
acids.  With  alkalies  it  yields  solutions  having  a. 
magnificent,  bright-green  fluorescence,  permanent 
even  in  very  dilute  solutions;  by  transmitted  light 
the  solutions  are  red.  Its  formula  is 

O(CeH3.OH)a.C.C8H4.O.CO  +  H3O. 


FLUORESCEIN  77 

The  sodium  or  potassium  salt  forms  a  yellowish- 
brown  powder,  soluble  in  alcohol  and  in  water  with 
intense  green  fluorescence. 

Application:  Fluorescein  was  recommended  for  use 
as  an  indicator  by  Kriiger.  It  is  very  useful  for 
titrating  in  dark-colored  liquids  in  which  color- 
changes  are  observed  only  with  difficulty,  because 
the  fluorescence  is  clearly  visible  so  long  as  the 
liquid  is  alkaline,  but  disappears  the  instant  the 
liquid  becomes  neutral  or  acid.  When  fine  white 
precipitates  are  formed  in  the  liquid,  however,  the 
fluorescence  may  be  masked ;  hence  the  precipitates 
(e.g.,  barium  sulphate)  are  allowed  to  settle  before 
determining  the  end  of  the  reaction. 

Fluorescein  is  serviceable  in  the  presence  of  car- 
bonic-acid gas,  as  this  does  not  affect  it.  It  is, 
however,  inapplicable  in  the  presence  of  acetic  acid, 
as  the  latter  dissolves  the  fluorescein  with  fluo- 
rescence, and  the  reading  would,  hence,  be  incor- 
rect. 

For  use,  a  solution  may  be  prepared  by  shaking 
together  I  Gm.  of  fluorescein  and  100  Cc.  of  diluted 
alcohol,  and  then  filtering.  The  solution  has  an 
orange-red  color;  it  does  not  keep  very  well. 
From  S  to  5  drops  are  used. 

Fluorescein  gives  fairly  good  results  in  titrating 
brucine,  cocaine,  co'deine,  coniine,  emetine,  nicotine, 
pelletierine,  quinine,  sparteine,  strychnine,  and  the- 
baine ;  it  is  very  good,  however,  with  atropine. 


7  IN DIC A  TORS 

FUCHSINE 

C30H18N3HC1 

Crimson 

ALKALIES  =  .  ACIDS  =  Yellow 

Colorless  in  Excess 

Synonyms:  Magenta;  Roseine;  Aniline  Red;  Rubin; 
Azaleine;  Solferino;  Fuchsiacine  ;  Erythrobenzeine  ; 
Harmaline;  Rubianite;  Rosaniline  Hydrochloride. 

Preparation:  Fuchsine  was  discovered  by  Natanson, 
of  Warsaw,  in  1856,  by  heating  aniline  with  ethy- 
lene  chloride  in  sealed  tubes  at  a  temperature  of 
200°  C.  In  1858  Hoffmann  also  obtained  it  by 
heating  carbon  bichloride  and  aniline  for  30  hours 
at  a  temperature  of  170°  to  180°  C.,  while  looking 
for  carbo-triphenyltriamine ;  he  considered  the  red 
color  due  to  an  impurity.  It  was  first  made  on  a 
practical  scale  by  Verguin,  in  1859,  by  substituting 
tin  bichloride  for  the  carbon  bichloride.  The  pro- 
cesses now  generally  followed  are  modifications  of 
those  patented  by  Hellman  in  1859  anc*  by  Med- 
lock  in  1860,  in  which  arsenic  is  used;  and  that 
patented  by  Coupier  in  1866,  in  which  nitrobenzene 
is  employed. 

Fuchsine  is  obtained  by  heating  a  mixture  of 
equal  molecular  weights  of  orthotoluidin,  para- 
toluidin,  and  aniline  with  a  concentrated  solution 
of  arsenic  acid  at  a  temperature  of  170°  to  180°  C. 
A  part  of  the  water  distills  over  during  the  opera- 
tion, which  lasts  from  seven  to  eight  hours.  The 


FUCHSINE  79 

mass  is  then  comminuted,  after  cooling,  and  ex- 
hausted  with  boiling  water  under  pressure ;  the 
arsenous  and  arsenic  acids  present  are  neutralized  by 
the  addition  of  lime.  Sodium  chloride  is  now 
added,  and  the  rosaniline  hydrochloride,  fuchsine, 
obtained  by  crystallization ;  it  is  then  recrystallized 
several  times,  but  cannot  be  obtained  entirely  free 
from  arsenic  acid. 

In  order,  however,  to  obtain  an  arsenic-free 
product,  a  mixture  of  aniline,  nitrobenzene,  nitro- 
toluene,  iron,  and  hydrochloric  acid  is  heated  as 
in  the  arsenic  process.  The  fuchsine  is  extracted 
from  the  fused  mass,  and  purified  as  already  de- 
scribed. 

Properties :  Fuchsine  occurs  in  the  form  of  crystals 
of  various  size  having  a  brilliant  green,  metallic 
color.  They  are  soluble  in  water  and  in  alcohol, 
yielding  intensely  crimson  solutions.  The  com- 
mercial preparation  is  most  generally  a  mixture  of 
pararosaniline  and  rosaniline  hydrochlorides,  the 
latter  predominating,  and  is  most  generally  found 
to  contain  arsenic,  which  should  always  be  tested 
for;  if  found  to  be  present,  the  preparation  should 
be  rejected. 

Pure  fuchsine  is  chemically  rosaniline  hydro- 
chloride,  C10H19N1HC1. 

Tests:  Fuchine  should  be  tested  for  arsenic  by 
Marsh's  apparatus. 


80  INDICA  TORS 

Mineral  impurities  maybedetectedbyincineration. 

Pure  fuchsine  is  decolorized  by  sulphurous  acid. 
Application :  A  solution  of  fuchsine  in  glacial  acetic 
acid  constitutes  a  delicate  reagent  for  nitrous  acid 
and  nitrites,  which  change  the  color  of  the  solution 
to  violet  first,  then  through  blue,  green,  yellow,  and 
finally  into  orange.  Nitric  acid  does  not  yield  the 
color  reactions. 

The  crimson  color  of  fuchsine  solutions  is 
changed  by  acids  to  yellow;  on  greatly  diluting  the 
solution,  however,  or  on  adding  an  alkali,  the  crirr- 
son  color  is  restored.  Ammonia,  however,  and  con- 
centrated caustic  alkalies  also  destroy  the  color, 
hence  fuchsine  is  not  satisfactory  for  use  as  an  indi- 
cator generally. 

Fuchsine-Sulphurous  Acid,  prepared  by  passing 
sulphurous  acid  gas  into  a  dilute  solution  of  fuchsine 
until  the  crimson  color  has  changed  to  a  pale  yel- 
low, has  been  found  to  be  a  very  delicate  reagent 
for  aldehydes  and  some  of  their  derivatives.  These 
all  afford  an  intense,  violet-red  color  with  it.  The 
solution  may  be  preserved  in  well-stoppered  bottles. 

GALLEIN 

(C,Ha.O.HO)3.(CO),.O.C8H4 

ALKALIES  =  Bright  Red  ACIDS  =  Pale  Brown 

Synonyms'.      Alizarin    Violet;     Anthracene    Violet; 
Pyrogallol  Phtalein  ;    Dechan's  Indicator. 

Preparation:      Gallein  was  discovered  by  Ad.  Baeyer 


GALLEIN  8 1 

in  1870.  It  is  prepared  by  heating  I  molecular 
weight  of  phtalic  anhydride  and  2  molecular  weights 
of  pyrogallol  at  a  temperature  of  from  190°  to  200°  C. 
for  several  hours,  dissolving  the  melted  mass  in  alco- 
hol, and  precipitating  by  adding  water.  The  pre- 
cipitate is  purified  by  repeated  solution  in  alcohol, 
reprecipitation  by  water,  and  finally  drying. 

Properties :  Purified  gallein  has  the  composition 
CaoH10O7,  and  forms  dark-reddish  crystals  having  a 
greenish  reflection,  or  a  brownish-red  powder.  It 
is  almost  insoluble  in  cold  water,  chloroform,  or 
benzene,  and  is  difficultly  soluble  in  hot  water, 
ether,  acetone,  or  glacial  acetic  acid.  It  is  but 
slightly  soluble  in  cold  alcohol,  but  is  very  readily 
soluble  in  hot  alcohol,  yielding  a  dark-red  solution. 
It  also  dissolves  in  cold  sulphuric  acid  unchanged, 
yielding  a  dark-red  solution. 

With  minute  quantities  of  alkalies,  lime,  or  baryta, 
it  yields  salts  which  dissolve  in  water  with  a  red 
color,  which  is  changed  to  a  blue,  however,  on 
adding  an  excess  of  alkali.  Acids,  even  sulphurous, 
precipitate  the  gallein  from  the  solution  unchanged. 
Gallein  also  dissolves  in  ammonia-,  lime-,  or  baryta- 
water,  with  a  violet  color;  the  color  of  the  am- 
moniacal  solution  remains  unchanged  by  heating. 

With  alumina  and  chromium  oxide  gallein  forms 
grayish-violet,  insoluble  lakes.  Reducing  agents 
convert  it  into  hydrogallein,  and  finally  into  gallin. 

Application  :     Gallein  was  proposed  by  Dechan  as  an 


82  2ND  1C  A  TORS 

indicator.  It  is  more  sensitive  towards  alkalies 
than  phenolphtalein,  and  may  be  advantageously 
used  in  titrating  many  alkaloids,  such  as  strychnine, 
morphine,  quinine,  cinchonidine,  and  atropine.  It  is  to 
some  extent  affected  by  carbonic-acid  gas.  Am- 
moniacal  salts,  when  present,  do  not  affect  it,  and 
it  is  serviceable  for  ammonia.  Organic  acids  may  be 
titrated  by  means  of  gallein,  as  the  indicator  is 
sharply  affected  by  them.  Carbonates  and  alkaloidal 
bases  .which  are  neutral  toward  phenolphtalein  yield 
a  rose-red  color  with  the  indicator. 

For  use  a  solution  of  I  :  1000  in  alcohol  may  be 
made,  about  10  drops  being  added  to  100  Cc.  of 
liquid  to  be  titrated. 

H^EMATOXYLIN 

C  «HM06-f  Aq 

ALKALIES  =  Blue  ACIDS  =  Red 

Source:  Haematoxylin  was  discovered  in  1811  by 
Chevreul,  who  named  it  Haematin,  in  the  heart 
wood  of  Hcematoxylon  campechianum  L.  (logwood ; 
Campeachy  wood),  one  of  the  Leguminosae  native 
to  Campeachy,  Yucatan,  Honduras  Bay,  and  several 
of  the  West  Indies. 

Preparation :  Haematoxylin  was  obtained  by  digest- 
ing ground  logwood  with  water  at  a  temperature 
of  from  50°  to  55°  C.  for  several  hours,  straining, 
evaporating  the  extract  to  dryness,  and  exhausting 
the  residue  with  strong  alcohol.  The  alcohol  was 


HJSMA  TOX  YLIN  83 

then   evaporated,  the   residual  liquid   mixed  with  a 
little  water,  and  the  whole  set  aside  to  crystallize. 

Erdmann,  in  1842,  obtained  the  haematoxylin 
from  the  commercial  extract  by  powdering  the 
latter,  mixing  it  with  some  sand,  and  exhausting 
with  repeated  portions  of  ether  containing  a  slight 
proportion  of  water.  The  ethereal  extract  was  then 
distilled  off,  and  the  remaining  syrupy  liquid  mixed 
with  water,  loosely  covered,  and  set  aside  to  crys- 
tallize. The  crystals  separated  in  a  few  days,  and 
were  then  collected,  washed  with  cold  water,  and 
recrystallized  from  hot  water,  or  from  water  to 
which  a  little  ammonium-  or  sodium-sulphite  had 
been  added. 

Properties:  Haematoxylin  forms  colorless,  or  slightly 
yellowish,  sweetish,  efflorescent,  shining  prisms 
containing  three  molecules  of  water  of  crystalliza- 
tion, or  occurs  as  rhombic  crystals  with  one  mole- 
cule of  water  of  crystallization.  The  crystals  have 
the  composition  C]6HMO8 -j- Aq. ,  and  are  soluble  in 
ether,  alcohol,  and  in  hot  water,  but  are  only  slightly 
soluble  in  cold  water.  They  melt  at  from  100°  to 
120°  C.  in  their  water  of  crystallization,  and  char  at 
higher  temperatures.  On  exposure  to  air  they  are 
rapidly  converted  into  haematein. 

Haematoxylin  is  very  soluble  in  a  solution  of 
borax;  and  with  warm  solutions  of  this  a  very  con- 
centrated, syrupy  solution  may  be  obtained,  which 
is  no  longer  alkaline,  but  neutral,  or  even  slightly 


84  1NDICA  TORS 

acid,  has  a  bluish  tinge,  and  does  not  deposit 
borax  on  adding  alcohol  or  alcohol  and  ether,  or 
yield  haematoxylin  crystals  on  evaporation.  Acids 
do,  however,  precipitate  the  haematoxylin  crystals 
with  one  molecule  of  water  of  crystallization ;  so  do 
also  certain  salts,  such  as  sodium-  or  ammonium- 
chloride,  precipitate  haematoxylin,  but  in  an 
amorphous  form. 

Boiling  hydrochloric  acid  or  potassa  lye  does  not 
decompose  haematoxylin;  nitric  acid  converts  it 
into  oxalic  acid,  and  concentrated  sulphuric  acid 
dissolves  it  with  brownish-yellow  color. 

With  alkalies,  haematoxylin  yields  solutions  hav- 
ing a  purple  color  changed  to  blue  by  the  action  of 
atmospheric  oxygen  which  converts  the  haematoxy- 
lyn  by  oxidation  into  haematein,  C10H13O, ,  the  color 
changing  finally  to  a  yellowish-brown. 

On  dry  distillation  haematoxylin  yields  pyrogallol 
and  resorcin ;  on  exposure  to  light  it  is  colored 
reddish. 

With  baryta  and  with  lead  acetate  it  yields  white 
precipitates;  with  copper  salts,  greenish-gray  pre- 
cipitates, which  soon  become  blue  on  contact  with 
air;  and  with  stannous  chloride  a  red  precipitate  is 
afforded. 

Haematoxylin  is  extremely  sensitive  to  ammonia, 
the  most  dilute  solutions  being  rapidly  affected 
by  it.  It  must  be  kept  in  well-closed  bottles, 
from  air  and  light. 


Jf^EMA  TOX  YL1N  8  5 

Tests :  Haematoxylin  should  always  be  tested  before 
use,  so  far  as  its  solubility  is  concerned.  A  small 
quantity  heated  on  platinum  foil  should  leave  no 
residue.  The  crystals  must  also  be  clean  and  not 
effloresced. 

Application :  Haematoxylin  is  not  well  adapted  for 
alkalimetry  or  acidimetry,  because,  during  warming 
with  an  alkali  carbonate,  it  undergoes  a  certain 
change,  and  upon  neutralization  exhibits  a  color 
entirely  different  from  what  it  originally  had,  which 
may,  hence,  be  the  cause  of  uncertainty  in  observa- 
tion. It  may  be  used  for  certain  substances,  such 
as  copper  salts,  alum,  chalk,  etc. 

Haematoxylin  is  one  of  the  best  of  indicators  for 
general  use  for  alkaloids,  and  particularly  for  atro- 
pine  and  emetine. 

Haematoxylin  Test-paper,  when  recently  made, 
is  also  very  serviceable.  (See  Test-papers). 


H^MATOXYLON 

ALKALIES  =  Blue  ACIDS  =  Red 

Synonyms  :  Logwood  ;  Campeachy  Wood. 
Source  :  Haematoxylon  is  the  name  usually  applied  to 
the  wood  of  Hcematoxylon  campcchianum  L.,  log- 
wood, one  of  the  Leguminosae  native  to  Cam- 
peachy,  Yucatan,  Honduras  Bay,  and  several  of 
the  West  Indies. 


86  INDICA  TORS 

Properties :  Haematoxylon  is  heavy,  hard,  and 
coarsely  grained,  brown  or  reddish-brown  within, 
and  blackish-red  or  bluish-black  externally.  The 
constituents  of  the  wood  are  hsematoxylin  (upon 
which  its  colorific  properties  depend),  a  volatile  oil, 
tannin,  resinous  substances,  various  salts  of  acetic 
acid,  calcium  oxalate,  potassium  chloride,  alumina, 
iron  and  manganese  oxides,  and  silica.  The  wood 
yields  to  water  its  coloring-matter,  and  affords  a 
dark-red  extract  which  affords  blue  precipitates  with 
lead  acetate,  lime-water,  and  alkali  carbonates; 
with  alum  a  violet  one;  with  nutgalls  a  black,  and 
with  iron  and  chromium  salts  a  violet-blue  to  black 
precipitate. 

Preparation:  Haematoxylon  is  generally  applied  as 
an  indicator  in  the  form  of  a  tincture  or  decoction, 
and  is  exceedingly  sensitive.  Since  the  wood  is 
very  easily  affected  by  both  light  and  air,  shavings 
from  the  inner  portion  of  a  billet  are  used,  and  the 
tincture  prepared  by  treating  the  shavings  with  a  45- 
per-cent.  pure  alcohol  for  24  hours  in  a  well-closed 
vessel  in  a  warm  place.  The  tincture  so  obtained 
is  filtered  through  glass  wool,  carefully  avoiding  any 
exposure  to  ammoniacal  vapors,  and  is  preserved  in 
small  vials  with  closely  fitting  glass  stoppers. 

Application :  A  tincture  so  prepared  is  one  of  the 
most  sensitive  of  reagents  for  free  alkalies  and  alka- 
line salts.  It  is  particularly  sensitive  to  ammonia, 


ff&MA  TOX  YLIN  / 

the  faintest  traces  of  which  suffice  to  afford  a  blue 
color, — a  fact  that  renders  the  application  of  the 
haematoxylon  as  an  indicator  somewhat  unsatisfac- 
tory because  of  the  difficulty  of  securing  an  abso- 
lutely ammonia-free  atmosphere  in  which  to 
operate. 

Haematoxylin  is  excellently  adapted  for  titrating 
the  alkaloids,  and  particularly  for  quinine  and  spar- 
teine. 

A  few  drops  of  the  tincture  added  to  a  solution 
containing  alkalies  or  alkaline  earths  affords  a  red, 
violet,  or  blue  color,  according  to  the  quantity  of 
alkali  present.  One  part  of  ammonia  in  500,000 
parts  of  water  affords  a  distinct  red  color.  Many 
metals,  particularly  iron  and  copper,  yield  blue  or 
bluish-violet  precipitates  with  haematoxylon  tinc- 
ture, even  when  other  reagents  fail  to  show  the 
minute  traces  present. 

An  aqueous  decoction  of  haematoxylon  is  simi- 
larly sensitive,  and  its  color  is  rapidly  changed  to  a 
violet  even  by  pure  calcium  carbonate,  chalk,  and 
marble  dust.  Both  the  tincture  and  the  decoction 
should  be  kept  only  in  an  acidulated  condition  be- 
cause of  their  exceeding  proneness,  when  in  neutral 
or  alkaline  solution,  to  become  colored. 

A  haematoxylin  test-paper  is  also  used  at  times, 
and  is  described  under  Test-papers. 


88  IND1CA  TORS 

INDIGOSULPHONIC   ACID 

(C.H,)2.(CO),.Ca.(NH),.(HSO,)a 


Synonyms:  Sulphindigotic  Acid;  Indigosulphuric 
Acid. 

Preparation  :  Solution  of  indigosulphonic  acid  for 
indicating  purposes  is  prepared  by  dissolving  pow- 
dered indigo  in  fuming  sulphuric  acid,  then  neutral- 
izing with  calcium  carbonate,  diluting  the  solution 
with  16  times  its  volume  of  water,  and  filtering  the 
blue  liquid  so  obtained. 

Application  :  The  blue  color  of  the  indigcsulphonic- 
acid  solution  is  not  disturbed  by  carbonates  of  the 
alkalies,  but  caustic  alkalies  change  the  color  to 
yellow,  hence  these  latter  may  be  determined  in  the 
presence  of  carbonates.  For  this  purpose,  I  or  2 
drops  of  the  indicator  solution  are  added  to  the 
solution  to  be  titrated,  and  the  acid  then  added. 
When  the  free  alkali  is  neutralized,  a  green  color 
forms,  which  gives  place  to  a  blue.  With  a  white 
dish,  the  color-change  is  seen  to  take  place  very 
sharply,  and  good  results  may  be  had.  The  indi- 
cator was  recommended  for  use  by  Engel  and 
Ville. 


INDIGO    CARMINE  89 

INDIGO   CARMINE 
(C«H,)a.(CO),.C..(NH),.(SOtNa), 

ALKALIES  —  Yellowish-brown  ACIDS  =  Blue 

Synonyms  :  Soluble  Indigo;  Indigo  Extract;  Blue 
Carmine;  Indigotine ;  Sodium  Indigotin-disul- 
phonic  Acid. 

Source  :  Indigo  carmine  is  the  blue  pigment  pre- 
pared from  indigo,  an  oxidation  product  of  indigo 
white,  or  indican,  a  constituent  of  the  sap  of 
various  species  of  the  Indigoferae,  chiefly  Indigofera 
tinctoria  L.,  /.  disperma,  I.  anil  L.,  and  7.  argentea 
L.,  Nat.  Ord.  Leguminosae.  These  are  found  in 
the  East  Indies,  Africa,  West  Indies,  Brazil, 
China  and  Hindostan. 

Preparation  :  According  to  Joclet,  indigo  carmine 
is  prepared  by  dissolving  i  part  of  powdered  indigo 
in  5  parts  of  concentrated  sulphuric  acid  heated  to 
50°  C.,  and  adding  to  the  solution  gradually  3.3 
parts  of  sodium  carbonate  dissolved  in  30  parts  of 
water.  The  mixture  is  stirred,  and,  after  12  hours, 
strained  through  a  woolen  cloth,  the  precipitate  of 
indigo  carmine  being  finally  washed  with  a  very 
small  quantity  of  water. 

Indigo  carmine  is  also  obtained  by  adding  I  part 
of  powdered  and  dried  indigo,  in  two  portions,  to  a 


90  INDICA  TORS 

mixture  of  4.5  parts  of  fuming  sulphuric  and  con- 
centrated sulphuric  acids,  stirring  constantly  and 
avoiding  a  rise  in  temperature.  When  the  mix- 
ture is  homogeneous,  it  is  kept  at  a  temperature  of 
50°  C.  for  a  week,  and  is  then  poured  into  10  parts  of 
water,  after  which  a  solution  of  10  parts  of  sodium 
chloride  having  a  sp.  gr.  of  1.170  is  next  added. 
The  precipitated  indigo  carmine  is  then  collected  by 
filtration,  washed  and  finally  dried. 

Properties  :  Indigo  carmine  is  the  sodium  salt  of 
indigotin-disulphonic  acid,  and  has  the  composition 
C18H8N3O,(SO8Na)2.  It  occurs  both  as  a  blue, 
pasty  mass,  and  as  a  blue,  dry  powder  soluble  in 
from  140  to  150  parts  of  water.  It  yields  a  blue 
solution,  the  color  of  which  is  changed  by  caustic 
soda  to  a  yellowish  brown,  and  restored  by  acids. 

Tests:  The  fitness  of  indigo  carmine  for  use  is 
recognized,  according  to  Mierzinski,  by  placing  a 
small  quantity  of  the  preparation  on  a  piece  of 
white  filtering-paper.  If  the  preparation  is  im- 
pure, a  green  ring  soon  forms  around  the  indigo 
carmine.  When  the  powdered  indigo  carmine  is 
to  be  tested,  it  is  first  stirred  with  a  little  boiling 
water  before  placing  on  the  filter-paper. 

Application:  Indigo-carmine  solution  is  used  in  the 
estimation  of  nitrites  and  of  chlorine,  both  of  which 
decolorize  it  on  boiling.  It  is  also  employed  for 
the  estimation  of  oxygen  and  of  tannin,  the  latter 


IODEOSINE  91 

particularly.  For  tannin,  Lowenthal  and  Schroder 
recommend  the  following  solution : 

30  Gm.  of  indigo  carmine,  in  dry  form,  are  dis- 
solved in  3  liters  of  diluted  sulphuric  acid  (i  :  5  by 
volume),  then  3  liters  of  distilled  water  added,  the 
whole  thoroughly  shaken  and  filtered. 

Care  must  be  exercised  that  only  a  good  quality 
of  indigo  carmine  be  used,  because,  when  a  poor 
quality  of  indigo  carmine  is  employed  when  titrat- 
ing with  potassium  permanganate  solution,  the  end 
of  the  reaction  is  not  clear,  as  the  greenish,  tint 
does  not  change  sharply  to  yellow,  but  changes 
through  reddish  and  brownish  tints  which  render 
it  impossible  to  note  the  end  of  the  reaction. 

IODEOSINE 

C8H4(CO.C6HaI20)20 

ALKALIES  =  Rose-red  ACIDS  =  Yellowish 

Synonyms:  Tetraiodofluoresceine;  Erythrosin  B.  ; 
Pyrosine  B.  ;  Dianthine  B. 

Preparation:  lodeosine  is  obtained  by  dissolving  6 
parts  of  fluorescein  in  a  hot  mixture  of  8  parts  of 
soda-lye  and  60  parts  of  water,  and  adding  to  this  a 
solution  of  24  parts  of  iodine  in  27  parts  of  soda- 
lye  mixed  with  60  parts  of  water;  to  this  mixture 
are  then  added  25  parts  of  glacial  acetic  acid.  The 
whole  is  boiled,  then  neutralized  with  caustic 
soda,  and  25  parts  of  hydrochloric  acid  are  added. 


92  INDICATORS 

The  precipitate  is  then  collected  and  purified  by 
dissolving  it  in  aqueous  ether,  shaking  out  with 
weak  caustic-soda  solution  and  reprecipitating  by 
adding  concentrated  soda-lye.  The  brick-red  pre- 
cipitate is  then  washed  with  alcohol,  and  crystal- 
lized from  hot  alcohol.  The  pure  sodium  salt  thus 
obtained  is  then  decomposed  by  hydrochloric  acid, 
and  the  precipitate  thoroughly  washed  and  dried  at 
a  temperature  of  about  120°  C. 

Properties:  lodeosine  occurs  as  a  brick-red  powder, 
almost  insoluble  in  water  and  in  cold  water,  but 
soluble  in  hot  alcohol  and  in  ether. 

Application:  Mylius  and  Forster  recommend  iodeo- 
sine  for  the  estimation  of  very  minute  quantities  of 
alkali ;  for  instance,  such  as  may  be  dissolved  out 
from  glass  on  contact  with  water.  For  this  purpose 
they  recommend  an  ethereal  solution  containing 
0.002  Gm.  per  liter  (i :  500,000). 

Titration  with  this  indicator  is  carried  out  by 
introducing  from  50  to  100  Cc.  of  the  liquid  to  be 
operated  on  into  a  stoppered  bottle  and  adding 
from  10  to  20  Cc.  of  the  ethereal  solution.  If  de- 
sired, 4  or  5  drops  of  a  I  :  10,000  aqueous  solution 
may  be  added  to  the  liquid,  and  ether  then  added. 
If  free  alkali  is  present,  even  in  mere  traces,  the 
aqueous  layer  soon  acquires  a  rose-red  tint,  whereas 
if  acids  are  added  the  ethereal  layer  becomes  colored 
yellowish. 


10DEOSWE  G  93 

lodeosine  is  one  of  the  best  of  indicators  for  use 
in  alkaloidal  estimations,  and  for  detecting  traces 
of  acids  or  of  acid  salts  in  so-called  neutral  chem- 
icals. 

H.  A.  Cripps  gives  the  following  process  for  us- 
ing the  indicator  for  alkaloids:  20  to  25  Mg.  of 
alkaloid  (or  alkaloidal  residue  from  a  drug  assay) 
are  dissolved  in  5  Cc.  of  «/2O  hydrochloric  acid, 
and  the  solution  diluted  to  measure  20  Cc.  with 
perfectly  neutral  water.  Four  drops  of  a  1 :  10,000 
aqueous  iodeosine  solution  are  now  added,  and  10 
Cc.  of  neutral  ether.  w/2OO  barium-hydrate  solution 
is  now  added  from  a  burette,  with  frequent  agitation 
until  the  aqueous  layer  has  assumed  a  rose  color. 
A  previous  titration  will  have  determined  the  value 
of  the  baryta  solution ;  and  the  difference  between 
the  two  titrations  will  indicate  the  alkaloid. 


IODEOSINE   G 

C,H4(CO.C«HaIONa)2O 
ALKALIES  =  Cherry-red        ACIDS  —  Brownish-yellow 

Synonyms:  Pyrosine  J.  ;  Dianthine  G.  ;  Jaune  d'Ori- 
ent ;  Erythrosine  G. ;  Diiodofluoresceine-Sodium 
(or  Potassium). 

Preparation :  lodeosine  G.  is  obtained  by  mixing 
solutions  of  6  parts  of  fluoresceine  and  16  parts  of 
iodine  in  20  parts  of  soda  lye  each,  and  precipita*- 


94  INDICA  TORS 

ing  with  20  parts  of  glacial  acetic  acid.  The  pre- 
cipitated diiodofluoresceine  is  then  converted  into  a 
sodium  (or  potassium)  salt,  which  is  purified  by 
recrystallization  from  hot  alcohol. 

Properties:  lodeosine  G.  forms  a  yellowish-brown 
powder  or  plates,  soluble  in  water,  and  yielding  a 
cherry-red  solution  free  from  fluorescence.  The 
color  of  the  solutions  is  changed  to  a  brownish- 
yellow  by  acids,  and  is  restored  to  red  by  alkalies. 

Application :  lodeosine  G.  or  lodeosine  (which  see) 
is  particularly  useful  in  alkaloidal  assays,  and  is  also 
serviceable  for  alkalies. 


IRON   AND   AMMONIUM   SULPHATE 

FERROUS  HALOGEN  SALTS  SILVER  SALTS 

=  Red  =  Red 

Fe2(S04)3.(NH4)2S04.24H20 

Synonym:   Ammonio-Ferric  Alum. 

Preparation:  240  Gm.  of  solution  of  ferric  sulphate 
(sp.  gr.  1.43)  are  added  to  a  solution  of  28  Gm.  of 
ammonium  sulphate  in  100  Gm.  of  warm  water. 
On  slowly  cooling  the  solution  crystals  are  ob- 
tained which  are  subsequently  freed  from  the 
mother  liquor,  washed  with  a  little  water  and 
dried. 

Properties:  Ammonio-ferric  alum  occurs  as  lilac  or 
violet  efflorescent  crystals  having  a  sour,  styptic 


LACMOID  95 

taste,  and  soluble  in  3  parts  of  water  and  in  0.8 
parts  of  boiling  water.  The  salt  is  affected  by 
light,  by  which  it  is  reduced  to  a  ferrous  condition, 
hence  it  should  be  kept  in  amber  bottles  or  in  a 
dark  place,  and  also  from  contact  with  air.  Its 
formula  is  Fe1(SO4)i.(NH4)1SO4.24H,O. 

Application:  Ammonio  ferric  alum  is  employed  as 
an  indicator  in  titrating  silver  salts  by  means  of 
decinormal  ammonium-  or  potassium-sulphocyanate 
solution,  and  similarly  for  titrating  ferrous  halogen 
salts,  using  silver  nitrate  and  a  sulphocyanate. 

LACMOID 

C13H9N04(?) 

ALKALIES  =  Blue  ACIDS  =  Red 

Synonyms:      Resorcin  Blue. 

Preparation:  Lacmoid  was  first  prepared  by  Wesel- 
sky  and  Benedikt,  in  1880.  It  is  obtained  by  heat- 
ing 20  parts  of  resorcin,  I  part  of  sodium  nitrite, 
and  I  part  of  distilled  water  on  an  oil-bath  to  110° 
C.,  at  which  temperature  the  reaction  becomes  quite 
active.  When  the  reaction  moderates,  the  heat  is 
raised  to  from  115°  to  120°  C.  ;  ammoniacal  vapors 
are  freely  disengaged  and  the  raspberry-red  mass  be- 
comes reddish-violet,  bluish-violet,  and  finally  blue. 
When  the  vapors  are  no  longer  disengaged,  the 
mass  is  dissolved  in  a  little  water,  and  precipitated 
by  hydrochloric  acid.  The  precipitate  is  then  col- 


IN  DIG  A  TORS 

lected,  washed  and  dried,  and  constitutes  the 
lacmoid  in  an  impure  form. 

Schaerges  recommends  preparing  the  lacmoid  by 
the  reaction  of  resorcin  on  sodium  nitrite  without 
the  addition  of  any  water,  and  at  a  temperature  not 
exceeding  no0  C.,  dissolving  the  product  in  a  little 
water,  and  removing  the  undecomposed  resorcin 
still  present  by  shaking  out  with  ether.  Schaerges 
claims  that  lacmoid  so  prepared  is  clearly  soluble 
in  all  proportions  in  water  and  in  dilute  alcohol,  but 
is  insoluble  in  ether. 

For  obtaining  a  perfectly  pure  lacmoid,  Forster 
recommends  treating  the  commercial  article  in  fine 
powder  with  boiling  water,  acidulating  the  blue 
solution  after  cooling  and  filtering,  with  hydro- 
chloric acid,  collecting  the  precipitate  after  a  few 
hours,  washing  it  with  a  little  cold  water,  and  dry- 
ing it  at  not  too  high  a  temperature;  or,  dissolving 
it  in  alcohol  and  evaporating  the  solvent. 

Lacmoid  solutions,  no  matter  how  carefully  pre- 
pared, are  more  or  less  prone  to  exhibit  a  violet 
tinge  which  may  prove  very  deceptive  to  other  than 
normal  eyes.  To  remedy  this  defect,  Forster  rec- 
ommends the  addition  of  5  Gm.  of  naphtol  green 
(Cassella  &  Co.)  to  3  Gm.  of  purified  lacmoid  ob- 
tained as  above,  and  dissolving  both  in  700 
Cc.  of  water  and  300  Cc.  of  alcohol.  Malachite 
green  had  formerly  been  proposed,  but  the  naphtol 
green  has  been  found  to  be  more  permanent,  and  to 


LA  CMOID  97 

yield  no  precipitate  with  lacmoid  (malachite  green 
does),  while  it  imparts  a  pure  blue  color  to  neutral 
and  alkaline  fluids,  which  is  changed  to  an  onion- 
red  with  acids.  The  sharpness  of  the  change  of 
color  is  greatly  enhanced  by  the  addition  of  the 
naphtol  green. 

Properties:  Lacmoid  occurs  as  a  glistening  brown 
or  dark-violet  powder,  amorphous  granules,  or  as 
blue-black  scales.  It  consists  principally  of  diazo- 
resorcin,  or  resazurin,  also  known  as  "  Weselsky's 
indicator."  Lacmoid  is  soluble  in  alcohol,  acetone, 
wood-alcohol,  pyroligneous  acid,  acetic  acid,  phenol, 
and  amyl  alcohol;  it  is  less  soluble  in  ether  and  in 
water,  and  insoluble  in  chloroform,  benzene,  and 
benzin. 

Its  constitution  is  unknown,  and  the  empirical 
formula  assigned  it  is  C12H9NO4. 

With  neutral  and  alkaline  liquids  lacmoid  yields 
handsome  blue  solutions  having  a  faint  violet  tinge, 
changed  by  a  mere  trace  of  acid  to  red.  The  solu- 
tions should  be  preserved  in  dark  bottles,  as  they 
are  .very  sensitive  to  light. 

Tests:  The  fitness  of  lacmoid  as  an  indicator  is  tested 
by  treatment  with  water.  If  but  little  or  no  color 
is  imparted  to  water,  the  sample  should  be  rejected. 
According  to  Traub,  a  few  drops  of  decinormal 
ammonia  suffice  to  clearly  show  the  blue  color  in  a 
solution  containing  I  12,000,000  of  the  indicator. 


9^  INDICA  TORS 

Application:  The  application  of  lacmoid  as  an  indi- 
cator is  very  similar  to  that  of  litmus.  It  is  useful 
for  titrating  both  caustic  alkalies  and  acids.  Aque- 
ous solutions  of  calcium  or  magnesium  bicarbonate 
affect  it  very  sharply.  Normal  alkali  sulphites  are 
strongly  alkaline,  and  bisulphites  are  neutral,  to 
lacmoid.  .  The  indicator  is  affected  by  the  hydrogen 
sulphide  liberated  in  titrating  sulphides,  hence  it  is 
unserviceable  for  them,  but  the  latter,  as  well  as 
carbonates,  sulphites,  phosphates,  arsenates,  and 
borates,  may  be  readily  and  accurately  titrated  by 
means  of  lacmoid  paper,  a  drop  of  the  liquid  being 
dropped  on  the  paper,  which  is  best  washed,  pre- 
.vious  to  use,  with  pure  distilled  water. 

To  acid  phosphates  and  arsenates  the  lacmoid  is 
neutral ;  nevertheless,  the  paper  is  most  service- 
able, and  shows  50$  of  the  alkali.  Towards  arsen- 
ous  acid  the  solution  is  neutral,  and  good  results 
are  obtainable  with  both  solution  and  paper.  Lac- 
moid paper  may  be  used  for  borax,  sodium  and 
ammonium  carbonates,  effervescent  preparations  of 
magnesium,  lithium,  and  other  carbonates,  etc.,  as 
well  as  for  the  alkali  of  the  alkali  silicates  (for  these 
latter  the  lacmoid  solution  answers  equally  well). 

Lacmoid  may  be  used  hot  for  titrating  the  alkali 
in  carbonates  or  bicarbonates,  but  the  change  of  color 
does  not  take  place  until  all  the  carbonic-acid  gas 
has  been  replaced.  Barium,  magnesium,  and  calcium 
carbonates  may  be  titrated  by  first  adding  an  excess 
of  acid,  and  then  titrating  back  with  alkali. 


LITMUS  %  99 

Lacmoid  solution  is  useless  for  sulphites  and 
sulphides,  but  is  applicable  for  borates.  Towards 
thiosulphates  it  is  neutral.  Borax,  silicic  acid, 
and  arsenic  acid  do  not  affect  the  indicator  in  the 
cold.  Arsenic  and  phosphoric  acids  behave  like 
monobasic  acids  towards  it. 

Potassium  and  sodium  bichromates  are  neutral  to 
lacmoid,  but  the  neutral  chromates  are  alkaline; 
hence  a  mixture  of  bichromate  with  chromate,  or  of 
chromic  acid  and  a  bichromate,  may  be  readily 
titrated  by  means  of  lacmoid. 

Oxalic,  acetic,  lactic,  tartaric,  and  nitric  acids,  as 
well  as  organic  acids  in  general,  cannot  be  titrated. 

The  sulphates  and  chlorides  of  iron,  copper,  and 
zinc,  which  are  all  more  or  less  acid  to  litmus,  are 
neutral  towards  lacmoid ;  hence  free  acids  present 
in  solutions  of  these  salts  may  be  estimated  with  it. 
For  alumina,  lacmoid  will  not  answer. 

Lacmoid  is  very  useful  for  titrating  atropine,  bru- 
cine,  cocaine,  codeine,  coniine,  emetine,  morphine, 
narcotine,  nicotine,  papaverine,  pelletierine,  quinine, 
strychnine,  thebaine,  and  veratrine. 

LITMUS 

ALKALIES  =  Blue  ACIDS  =  Red 

Synonym :     Lacmus. 

Source  :     Litmus   is  a  pigment  obtained  principally 
from     Rocella     tinctoria     Acharius,    but    also   from 


100  INDICATORS 

Lecanora  tartarea  Ach.,  R.  fuciformis  Ach.,  Vario- 
laria  dealbata,  etc.,  lichens  found  growing  some- 
times on  trees,  sometimes  on  cliffs,  on  the  coasts  of 
the  Mediterranean  Sea,  Spain,  France,  Holland, 
England,  and  Sweden,  and  also  on  the  Canary 
Islands,  Orkney  Islands,  and  Corsica. 

Preparation  :  Litmus  does  not  exist  as  such  in  the 
plants.  By  the  action  of  ammonia  and  air  alone  on 
the  lichens,  a  peculiar  substance,  orcein,  discovered 
by  Robiquet  in  1829  is  formed  ;  but  when  potassa 
is  permitted  to  act  in  conjunction  with  the  other 
substances,  a  new  coloring-matter  is  the  result,  a 
compound  of  chiefly  azolitmin  and  potassa.  Hence, 
the  lichens  are  ground,  and  mixed  with  ammonia 
and  potassa  ;  they  are  then  permitted  to  ferment 
until  the  mixture  acquires  a  violet  color,  when  lime, 
potassa,  and  generally  urine  also,  are  added,  and  the 
whole  allowed  to  stand  for  2  or  3  weeks,  or  until  a 
blue  color  has  been  acquired.  Chalk  and  gypsum 
in  variable  quantities  are  then  added,  and  the 
mixture  is  strained  through  a  hair  sieve,  and 
finally  formed  into  little  cakes  or  cubes. 

Properties  :  Litmus  occurs  in  the  form  of  small, 
light,  friable,  finely  granular  cakes  or  cubes  poses- 
sing  a  handsome,  violet-blue  color.  It  has  a 
peculiar,  characteristic  odor  recalling  that  of  indigo, 
and  has  a  pungent  and  somewhat  saline  taste.  It 
is  partly  soluble  in  water  with  a  blue,  and  in  dilute 


LITMUS  IOI 

alcohol  with  a  purplish-blue,  color,  which  is  changed 
to  red  by  acids.  Its  principal  coloring-matter) 
and  the  one  on  which  its  value  as  an  indicator 
depends,  is  azolitmin,  which  was  discovered  by 
Kane  in  1841  (see  Azolitmin). 

Tests  :  The  quality  of  the  litmus  of  the  market  is 
apt  to  vary  greatly,  hence  the  article  should  in- 
variably be  tested  when  a  new  lot  is  purchased. 
For  the  test,  equal  quantities  of  the  litmus  to  be 
tested  and  an  article  known  to  be  good  are  weighed, 
and  both  treated  with  equal  volumes  of  distilled 
water  for  12  to  24  hours,  shaking  every  now  and 
then.  When  the  mixtures  have  settled,  they  are 
filtered,  and  the  colors  then  compared. 

A  still  better  plan  is  to  heat  the  cold  aqueous 
extract  so  obtained  to  boiling,  and  then  to  add 
hydrochloric  acid  by  drops  until  a  permanent  onion- 
red  color  is  had  on  boiling  for  6  to  8  minutes. 
The  solution  is  then  rapidly  cooled,  and  mixed 
with  an  equal  volume  of  alcohol.  The  tincture 
so  obtained  is  then  tested  as  to  its  sensitiveness  to 
acids  and  alkalies.  This  should  be  such  that  when 
sufficient  of  the  tincture  is  added  to  250  Cc.  of 
recently  boiled  and  cooled  distilled  water  to  color 
the  latter  a  distinct  violet  (indicating  neutrality),  a 
solution  is  had  which  is  sharply  changed  to  an 
onion-red  or  pure  blue  by  one  drop  of  decinormal 
hydrochloric  acid  or  decinormal  alkali  respectively. 
On  standing  for  a  minute  or  so,  either  solution  will 


102  »  INDICATORS 

acquire  a  violet  tint.  In  these  solutions  two  drops 
of  the  decinormal  acid  will  give  a  permanent  onion- 
red  with  the  blue  solution ;  whereas  two  drops  of 
the  decinormal  alkali  suffice  to  give  a  permanent 
blue  with  the  red  solution. 

0.2  Cc.  of  a  ic-per-cent.  solution  of  purified 
litmus  added  to  IOO  Cc.  of  distilled  water  should 
require  about  0.05  Cc.  of  decinormal  hydrochloric 
acid,  or  o.  I  Cc.  of  decinormal  potassa  to  effect 
changes  of  color. 

Application  :  Since  the  value  of  the  litmus  as  an 
indicator  depends  entirely  on  the  azolitmin  present, 
and  since  the  latter  is  accompanied  by  three  other 
coloring-matters  which  detract  from  its  sensitive- 
ness because  yielding  violet  tints,  it  is  desirable,  in 
preparing  solutions  for  titrimetric  observations,  to 
effect  a  separation  of  the  coloring-matters  so  that 
only  azolitmin  will  be  present  in  the  solution.  This 
separation  is  effected  by  exhausting  the  coarsely 
powdered  litmus  with  successive  portions  of  hot 
alcohol,  in  which  azolitmin  is  insoluble,  but  in  which 
the  others  are  soluble.  The  residue  is  then 
digested  with  cold  dilute  acid,  in  order  to  remove 
the  excess  of  free  alkali  present,  and  then  with  five 
times  its  weight  of  boiling  water,  which  dissolves 
out  the  azolitmin.  The  solution  is  then  filtered. 

Of  the  solution  made  as  above  detailed1,  about   5 

drops  are  added  to  100  Cc.  of  liquid  to  be  titrated. 

Litmus  solution    is    best  kept   in    comparatively 


LITMUS  103 

wide-mouthed,  half-filled  bottles,  closed  by  a  plug 
of  cotton  to  keep  out  dust,  but  not  air.  In  the 
absence  of  the  latter,  the  solution  undergoes  a 
peculiar  fermentation,  evidenced  by  a  disagreeable 
odor  and  loss  of  color.  An  apparently  spoiled 
solution  recovers  its  original  color  and  valuable 
properties,  however,  on  exposure  to  air  in  a  shallow 
dish  ;  it  does  not  require  filtering  or  boiling, 
simple  exposure,  with  exclusion  of  dust,  sufficing. 
The  solution  should  not  be  kept  in  an  acidified  con- 
dition, as  it  is  then  very  prone  to  become  mouldy. 
Many  substances  have  been  proposed  for  the  pur- 
pose of  preserving  the  solutions,  among  others, 
carbolic  acid.  No  special  advantages  have,  how- 
ever, been  found  to  accrue  from  their  use,  and  the 
practice  of  adding  preservatives  is  not  general. 

Litmus  yields  a  deep  blue  color  with  alkalies,  and 
an  onion-skin  red  with  acids.  Carbonates  of  the 
alkalies  also  produce  the  blue  color,  and  the  indica- 
tor may  therefore  be  used  for  titrating  hydroxides 
of  the  alkalies  only  when  no  carbonates  are  present. 
With  carbonates  and  bicarbonates,  it  can  only  be 
used  when  the  liberated  carbonic-acid  gas  is  ex- 
pelled from  the  solution  by  boiling,  as  the  dissolved 
gas  would  otherwise  cause  the  red  color  to  persist 
even  though  the  liquid  is  alkaline,  and  thus  prove  a 
source  of  error. 

When  a  diluted  mineral  acid  is  added  drop  by 
drop  to  a  solution  of  a  carbonate  of  an  alkali  to 

CALIFORNIA   COLLEGI 
of  PHARMACY  - 


104  1NDICA  TORS 

which  litmus  has  been  added,  no  change  of  color 
takes  place  until  from  6o#  to  64$  of  the  carbonate 
has  been  neutralized,  when  the  solution  assumes  a 
purplish  or  violet  color.  On  now  heating  the  solu- 
tion, carbonic-acid  gas  is  copiously  evolved,  and  on 
the  continued  addition  of  acid  to  the  boiling  solu- 
tion, the  latter  acquires  an  onion-red  color  as  soon 
as  the  least  excess  of  acid  is  added.  The  color  is 
permanent,  not  being  affected  by  the  boiling;  and 
the  end  of  the  reaction  is  readily  recognized  when 
the  color,  at  the  point  where  the  dropping  acid 
reaches  the  solution,  cannot  be  distinguished  from 
that  possessed  by  the  solution  in  general. 

The  end  of  the  reaction  is  very  sharp  with  caus- 
tic alkalies,  alkaline  earths,  and  their  carbonates ; 
and  also  with  sulphides,  but  with  these  the  hydro- 
gen sulphide  liberated  must  also  be  driven  off  by 
boiling,  as  with  carbonic-acid  gas. 

Litmus  is  fairly  good  for  titrating  ammonia,  and, 
under  certain  conditions,  for  ammonium  carbonate 
also.  With  silicates  of  the  alkalies  the  reaction  is 
very  sharp.  With  borates  of  the  alkalies  and  of 
magnesium,  as  well  as  with  the  sulphates  and  phos- 
phates of  the  alkalies,  and  also  arsenates,  the  end 
of  the  reaction  is  uncertain,  as  the  change  of  color 
is  too  gradual.  With  arsenites,  however,  the 
change  is  sharp. 

With   sulphites  the  colors  yielded  are  somewhat 


LITMUS  105 

indefinite,  but  the  change  is  very  sharp  and  certain 
the  moment  saturation  is  complete. 

Litmus  is  useless  for  titrating  tartaric  and  citric 
acids,  but  is  serviceable  for  benzoic  and  oxalic 
acids.  The  indicator  may  also  be  employed  in  ti- 
trating the  acids  in  the  normal  salts  of  quinine, 
strychnine,  morphine,  narceine  and  papaverine,  as 
these  are  neutral  to  litmus.  Caffeine,  narcotine,  and 
theobromine  alkaloids  are  neutral  to  litmus,  but  their 
salts  behave  like  a  corresponding  quantity  of  free 
acid.  In  titrating  quinine,  oxyacids  are  unsuitable 
for  use,  because  they  cause  too  much  fluorescence, 
hence  decinormal  hydrochloric  acid  is  most  suitable. 
Toward  emetin,  litmus  is  neutral. 

Litmus  is  most  serviceable  for  indicating  the 
neutrality  of  milk  when  the  acidity  of  the  latter  is 
neutralized  previous  to  the  estimation  of  fat.  It  is 
also  useful  for  estimating  the  acidity  of  urine. 

Aniline,  toluidine,  and  quinoline  are  neutral  to 
litmus,  and  so  are  also  anhydrides  and  concentrated 
anhydrous  acids.  With  these  latter  the  change  of 
color  occurs  only  when  water  is  present.  Litmus 
is  not  well  adapted  for  use  by  gas-  or  lamp-light, 
hence  when  it  is  desired  to  perform  titrations  at 
night  with  it,  the  use  of  a  sodium-flame  will  be 
found  to  be  necessary.  The  sodium-flame  may  be 
obtained  by  placing  on  a  retort  ring  a  circular  piece 
of  asbestos,  in  the  center  of  which  a  small  hole 
has  been  cut  out.  Through  this  hole  the  flame 


106  JNDICA  TORS 

from  a  Bunsen-burner  is  allowed  to  pass,  while  it 
touches  the  margin  of  the  hole.  Around  the  mar- 
gin some  sodium  chloride  or  borax  is  sprinkled ; 
or,  the  margin  may  be  impregnated  with  a  concen- 
trated solution  of  sodium  chloride.  In  the  mono- 
chromatic light  so  obtained,  the  onion-red  color  of 
the  litmus  appears  perfectly  colorless,  while  the 
blue  is  distinct  and  appears  black. 

LUTEOL 

CeH,.OHa(NC).(CeH6)3Cl 

ALKALIES  =  Yellow  ACIDS  =  Colorless 

Synonyms:  Oxychlordiphenylquinoxaline;  Auten- 
rieth's  Indicator. 

Preparation  :  Luteol  is  prepared  by  heating  one 
molecular  weight  of  ethoxyphenylenediamine  with 
one  molecular  weight  of  benzile  in  alcoholic  solu- 
tion, and  recrystallizing  the  precipitated  ethoxy- 
phenylquinoxaline  from  alcohol.  This  is  then  heated 
with  phosphorus  pentachloride  to  a  temperature  of 
from  70°  to  90°  C.  in  a  paraffin  bath,  when  some  of 
the  chlorine  enters  into  the  compound,  while  phos- 
phorus trichloride  and  hydrochloric  acid  distil  off. 
The  ethoxychlordiphenylquinoxaline  so  obtained 
is  next  heated  to  from  180°  to  200°  C.  with  hydro- 
chloric acid  in  a  sealed  tube,  when  the  alkyl, 
ethylene  chloride,  is  split  off.  The  residue,  which 


LUTEOL 

constitutes  the  luteol,  is  then  purified  by  repeated 
recrystallization   from  alcohol. 

Properties  :  Luteol  pccurs  as  fine,  woolly,  yellowish 
needles  that  melt  at  246°  C.,  and  sublime  without 
decomposition  at  higher  temperatures.  It  is  insol- 
uble in  water,  and  sparingly  soluble  in  cold  alcohol, 
but  is  readily  soluble  in  hot  alcohol  and  in  ether. 
In  concentrated  sulphuric  acid  it  dissolves  with  a  red 
color,  but  is  reprecipitated  by  the  addition  of  water. 
It  is  sparingly  soluble  in  concentrated  hydrochloric 
acid,  but  is  perfectly  insoluble  in  the  diluted  acid. 
It  is  readily  soluble  in  alkaline  solutions,  yielding  a 
yellow  color.  Chemically,  luteol  is  a  phenol,  its 
formula  being:  C.H,.OHi(NC).(CaH§)1Cl. 

Application  :  Luteol  was  recommended  as  an  in- 
dicator by  W.  Autenrieth.  In  point  of  sensitiveness 
it  far  exceeds  both  litmus  and  phenolphtalein ;  5  to 
10  Cc.  of  a  solution  containing  I  drop  of  dilute 
soda  lye  in  a  liter  are  distinctly  colored  yellow  by 
a  few  drops  of  an  alcoholic  luteol  solution.  To 
ammonia,  luteol  is  even  more  sensitive  than  is 
Nessler's  solution,  as  5  to  10  Cc.  of  a  solution  con- 
taining I  drop  of  ammonia  water  per  liter  are 
colored  yellow  immediately,  whereas  with  Nessler's 
test  a  reaction  was  obtained  only  after  some  time. 

Luteol  expels  carbonic  acid  from  carbonates,  and 
the  acid  character  of  the  phenol  is  greatly  increased 
by  the  introduction  of  the  chlorine  atom  into  the 
preparation. 


IO8  IN DIC A  TORS 

It  is  superior  to  phenolphtalein  in  that  it  may  be 
used  in  the  presence  of  ammonia ;  and  better  than 
litmus  because  no  intermediate  colors  appear  during 
the  change,  hence  insuring  greater  accuracy.  The 
yellow  color  produced  by  alkalies  is  discharged  by 
acids,  the  solution  becoming  colorless. 

Solution  of  luteol  for  indicating  is  prepared  by 
dissolving  I  part  of  the  substance  in  300  parts  of 
alcohol.  Of  this  solution  from  4  to  8  drops  are 
added  to  100  Cc.  of  the  solution  to  be  titrated. 


MALLOW 

ALKALIES  =  Green  ACIDS  =  Red 

Source :  The  purple  flowers  of  several  species  of 
Mallow  yield  a  pigment  that  has  been  applied  as 
an  indicator.  The  species  from  which  the  pigment 
is  most  generally  obtained  are  Althcea  rosea  Cava- 
nilles  (Alcea  rosea  Linn.),  hollyhock;  Malva  sylves- 
tris,  common  mallow;  and  Malva  vulgaris.  The 
mallows  are  biannual  plants,  and  are  indigenous  to 
the  Orient,  but  are  found  cultivated  over  all  of 
southern  and  central  Europe. 

Preparation:  The  pigment  of  the  mallow  flowers  is 
extracted  by  exhausting  the  latter  with  hot  water, 
or  with  alcohol,  and  carefully  evaporating  the 
solvents. 


MALLOW 

Properties  :  The  aqueous  extract  of  the  hollyhock  is 
violet-red  in  color,  the  margins  of  the  solutions 
presenting  a  dark-violet  color,  whereas  the  alco- 
holic extract  is  purplish-red,  and  deposits  the  pig- 
ment, on  evaporation  of  the  alcohol,  in  the  form 
of  a  blackish,  nitrogenous  substance.  Solutions  of 
the  pigment  are  colored  a  fine  red  by  acids,  and 
green  by  alkalies,  in  which  respect  it  is  closely 
allied  to  the  pigment  obtained  from  the  common 
Dahlia,  and  with  which  it  is,  in  fact,  believed  to  be 
identical.  Alum  yields  with  the  pigment-solution 
a  lilac  color,  and  baryta-water  causes  the  gelatiniza- 
tion  of  the  solution  with  a  green  color. 

The  flowers  of  Malva  vulgaris  yield,  when  ex- 
tracted with  water,  a  reddish-brown  infusion  which 
is  colored  a  wine-red  by  acids ;  alkalies,  however, 
deepen  the  color  at  first,  but  afford  a  reddish- 
yellow  later.  With  this  infusion  alum  and  baryta- 
water  yield  yellowish-white  precipitates. 

Application :  Mallow  pigment  is  now  but  seldom 
used  as  an  indicator.  It  is,  however,  largely  used 
for  intensifying  the  color  of  red  wine.  A  test- 
paper  is  still  sometimes  used  (see  under  Test- 
Papers). 


1 i  o  JATD  ic A  roxs 

MESITYLENE-QUINONE 

C6H4(CH,)2OH.O 

ALKALIES  =  Reddish-violet  ACIDS  —  Yellow 

Synonyms  :  Oxymeta  -  xyloquinone  ;  Trimethylben- 
zene-quinone  ;  Oxy-iso-xyloquinone ;  Fittig's  Indi- 
cator. 

Preparation:  Mesitylene  -  quinone  is  obtained  by 
subjecting  a  mixture  of  5  Gm.  of  diamidomesitylene 
hydrochlorate,  250  Gm.  of  water,  12  Gm.  of  sulphu- 
ric acid,  and  I  Gm.  of  potassium  bichromate  to  dis- 
tillation so  long  as  a  yellow  distillate  is  received. 
When  this  ceases  I  Gm.  more  of  potassium  bichro- 
mate is  added  to  the  mixture,  and  water  to  make 
up  the  original  volume,  and  the  whole  again  sub- 
jected to  distillation.  The  distillates  are  then 
mixed  and  shaken  out  with  ether,  which  removes 
the  mesitylene-quinone,  and  deposits  it,  on  evapo- 
ration. 

Properties:  Mesitylene-quinone  forms  orange-red 
needles  which  are  very  readily  soluble  in  alcohol 
and  in  ether,  quite  readily  soluble  in  hot  water,  and 
difficultly  so  in  cold  water.  It  is  easily  volatilized 
by  steam,  melts  at  103°  C.,  and  sublimes  in  the 
form  of  deep,  golden-yellow,  long  needles.  Its 
formula  Is  believed  to  be  C.H4(CH8),OH.O. 


METHYL    ORANGE  III 

Application  :  Mesitylene-quinone  is  exceedingly  sen- 
sitive to  alkalies,  being  colored  by  them  a  reddish 
violet.  It  is  far  more  sensitive  than  litmus,  and  is 
colored  even  by  calcium  carbonate  and  by  spring 
water.  It  has  been  employed  in  testing  the  latter. 

METHYL   ORANGE 

C6H4.N(CH8)2.N,.C6H4.SOaNa 

ALKALIES  —  Yellow  ACIDS  =  Red 

Synonyms  :  Dimethylaniline  Orange  ;  Mandarin 
Orange;  Tropaeolin  D.  ;  Orange  III;  Pointer's 
Orange  III;  Helianthine;  Gold  Orange;  Sodium 
(or  Ammonium)  Dimethylaniline -azobenzene-sul- 
phonate  ;  Parasulphobenzene  -  azodimethylaniline 
Sodium  (or  Ammonium) ;  Sodium  (or  Ammonium) 
Dimethylamidoazobenzene  -  sulphonate  ;  Lunge's 
Indicator. 

Preparation:  Methyl  orange  is  obtained  by  the 
action  of  diazobenzenesulphonic  acid  on  dimethyl- 
aniline,  and  converting  the  acid  so  obtained  into 
its  sodium  or  ammonium  salt.  It  may  be  pre-. 
pared  by  dissolving  10  parts  of  aniline,  13  parts  of 
dimethylaniline,  and  23  parts  of  hydrochloric  acid 
in  360  parts  of  water,  and  adding  gradually  a  solu- 
tion of  7.4  parts  of  sodium  nitrite  and  4  parts  of 
caustic  soda  in*  54  parts  of  water.  The  precipitate 
is  collected,  dissolved  in  hydrochloric  acid,  and 
reprecipitated  by  caustic  soda.  It  is  again  col- 


1 1 2  INDICA  TORS 

lected,  washed,  and  crystallized  from  hot  alcohol. 
The  dimethyl-amidoazobenzene  so  obtained  is  then 
converted  into  a  sulphonate  by  dissolving  it  in  20 
times  its  weight  of  concentrated  sulphuric  acid, 
pouring  the  solution  into  cold  water,  and  dissolving 
the  precipitate  in  sufficient  caustic-soda  solution ; 
the  solvent  is  then  evaporated,  and  yields  the 
sodium  salt. 

Properties:  Methyl  orange  occurs  as  an  ocher-yellow 
powder,  readily  soluble  in  hot  water,  moderately 
soluble  in  cold,  and  only  slightly  soluble  in  alcohol, 
but  more  so  in  dilute  alcohol. 

Tests:  There  are  on  the  market  a  number  of  prep- 
arations bearing  the  name  "  methyl  orange  "  which 
are  totally  unfit  for  use  as  indicators;  hence  every 
new  sample  must  be  carefully  tested.  Alfred  H. 
Allen  states  that  when  any  doubt  exists  as  to  its 
fitness,  the  suspected  methyl  orange  should  be 
purified  by  precipitating  the  hot  concentrated  solu- 
tion with  hydrochloric  acid,  and,  after  washing  the 
precipitate,  dissolving  it  in  ammonia.  The  follow- 
ing are  the  tests  given  whereby  a  good  methyl 
orange  may  be  identified,  and  differentiated  from 
other  oranges : 

The  aqueous  solution  is  orange-yellow,  and  is 
not  precipitated  by  alkalies  (Orange  I  gives  a  red- 
dish-brown ;  Orange  II  a  brownish-red). 

Hydrochloric  acid  precipitates  from  hot,  concen- 


METHYL    ORANGE  113 

trated  solutions  the  free  sulphonic  acid,  as  micro- 
scopic needles,  which  soon  become  lustrous  plates 
or  prisms  having  a  violet  reflection  (Orange  I  gives 
a  yellowish-brown  precipitate;  Orange  II  gives  a 
brownish-yellow  precipitate). 

With  concentrated  sulphuric  acid  a  reddish  or 
yellowish-brown  solution  is  afforded,  the  color  of 
which  is  yellow  in  thin  layers,  and  a  splendid  red 
on  copious  dilution. 

Barium-  or  calcium  chloride  affords  no  precipitate 
(Orange  I  yields  a  red  precipitate  with  calcium 
chloride). 

Basic  lead  acetate  precipitates  the  methyl  orange 
as  an  orange-yellow  powder  (Acid  Yellow  is  not 
precipitated). 

Magnesium  sulphate  precipitates  the  indicator 
from  dilute  solutions  in  the  form  of  microscopic 
crystals. 

With  gold  chloride  methyl  orange  gives  a  red 
color  (Orange  IV  gives  a  violet,  then  green  color). 

Application :  Methyl  orange  was  recommended  as  an 
indicator  by  Lunge  in  1881.  For  titration,  a  solu- 
tion is  prepared  by  dissolving  I  Gm.  of  methyl 
orange  in  1000  Cc.  of  water.  Of  this  solution  4  or 
5  drops  are  added  to  100  Cc.  of  the  solution  to  be 
titrated.  The  color  of  the  solution  is  yellow,  and 
remains  unaffected  by  alkalies  or  carbonates  of  the 
alkalies,  but  is  changed  by  acids  to  a  handsome  red. 
Methyl  orange  is  an  excellent  indicator,  but  re- 


114  INDICATORS 

quires  a  practised  eye,  as  well  as  considerable  care, 
in  its  use,  as  the  readings  are  apt  to  be  misleading 
on  account  of  the  sulphates  or  chlorides  formed 
during  titration ;  these  have  an  influence  on  the 
sharpness  of  the  change,  an  onion-red  color  being 
first  formed  when  acids  are  added.  The  final  col- 
oration is  also  not  quite  so  intense  as  with  phe- 
nolphtalein  ;  and  if  more  than  4  or  5  drops  of  the 
solution  be  used  to  100  Cc.  of  fluid  in  order  to 
obtain  sharper  results,  there  is  a  diminution  in  the 
sensitiveness,  hence  an  excess  must  be  avoided. 

In  titrating  alkaline  solutions,  the  yellow  color 
first  changes  suddenly  to  a  yellowish-red  on  ap- 
proaching neutralization,  and  the  fine  red  develops 
immediately  on  the  further  addition  of  a  drop  of 
the  normal  acid  employed. 

Methyl  orange  possesses  comparatively  strong 
acid  properties,  therefore  only  strong  acids  can  be 
titrated  by  means  of  it,  and  hence,  also,  it  is  much 
more  sensitive  to  alkalies  than  to  acids. 

Carbonic,  boric,  silicic,  sulphydric  and  arsenous 
acids,  as  well  as  the  ordinary  organic  acids,  oxalic, 
tartaric,  acetic,  citric,  carbolic,  etc.,  and  the  fatty 
acids,  oleic,  palmitic,  stearic,  etc.,  yield  no  red  color 
with  the  indicator.  Hence  oxalic  or  acetic  acid 
cannot  be  used  with  methyl  orange  for  titrating 
alkalies. 

Ammoniacal  salts,  sulphates,  nitrates,  and  chlo- 
rides seriously  diminish  the  sensitiveness  of  the 


METHYL    ORANGE  11$ 

indicator;  their  absence  should  therefore  be  assured 
in  order  not  to  increase  the  liability  of  error  which 
the  formation  of  these  salts  during  titration  already 
induces. 

Sulphites  and  hyposulphites  of  the  alkalies  have 
no  effect  on  the  color,  as  they  are  neutral.  Sul- 
phites may  be  titrated  only  if  no  carbonate  is  pres- 
ent, otherwise  the  readings  are  apt  to  be  inaccurate. 
On  titrating  sulphites  with  methyl  orange,  the  red 
color  is  yielded  when  a  bisulphite  is  formed. 

Nitrites  of  the  alkalies  (which  are  neutral  to 
rosolic  acid,  phenacetolin,  litmus,  and  phenolphta- 
lein)  either  prevent  the  red  cclor  or  rapidly  dis- 
charge it  in  acid  solutions,  with  decomposition  of 
the  indicator.  Nitrous  acid  also  decomposes  the 
indicator. 

Arsenic  and  phosphoric  acids,  when  titrated  with 
methyl  orange,  behave  like  monobasic  acids;  i.e., 
they  are  rendered  neutral  to  it  when  one-third  of  the 
acid  has  combined  with  the  base  used  in  titrating, 
the  end  reaction  being  very  sharply  defined  (with 
phenolphtalein  these  acids  indicate  neutrality  when 
two-thirds  of  the  acids  have  entered  into  combina- 
tion). Hence  monophosphates  and  monoarsenates 
afford  alkaline  reactions  with  methyl  orange. 

Arsenous  acid  is  neutral  to  methyl  orange ;  hence 
it  and  arsenites  can  be  accurately  titrated,  the 
reaction  being  very  sharp. 

Methyl  orange  answers  well  for  ammonia,  but  is 


Il6  INDICATORS 

useless  for  lactic,  citric,  tartaric,  succinic,  butyric, 
acetic,  and  in  fact  almost  all  organic  acids. 

The  indicator  is  very  serviceable  for  estimating 
sulphides,  carbonates,  and  bicarbonates  of  the  alka- 
lies, as  the  liberated  hydrogen  sulphide  or  carbonic- 
acid  gas  does  not  affect  its  color.  It  is  also  the 
best  indicator,  probably,  for  estimating  the  sodium, 
potassium,  ammonium,  calciu'm,  and  magnesium,  bo- 
rates,  as  the  liberated  boric  acid  has  no  influence 
on  the  color. 

Methyl  orange  is  serviceable  for  titrating  the 
silicates  of  the  alkalies  ;  it  is  also  useful  for  estimat- 
ing mineral  acids  in  the  presence  of  fatty  acids,  as 
the  latter  do  not  affect  the  color  of  alkaline  solu- 
tions. It  is  also  useful  for  estimating  free  acids 
present  in  solutions  of  metallic  salts,  or  in  alum, 
cupric  chloride,  ferrous  sulphate,  etc. 

The  indicator  is  also  applicable  for  the  estimation 
of  alkaloids,  such  as  strychnine,  quinine,  cinchonidine, 
atropine,  and  especially  for  morphine. 

The  use  of  alcoholic  solutions  must  be  avoided 
when  methyl  orange  is  used  as  the  indicator,  other- 
wise the  readings  will  be  erroneous. 

Methyl  orange  is  unsuitable  for  titrating  alkali  in 
the  presence  of  alumina,  as  the  aluminum  sulphate 
formed  during  titrating  is  neutral  to  it.  In  this 
case  only  the  alkali  and  alumina  together  can  be 
determined,  and  the  alumina  determined  by  the 
difference  after  again  titrating,  using  phenolphtalein 


METHYL    ORANGE 

(the  latter  is  affected  by  aluminum  sulphate).  The 
operation  is  best  conducted  in  lukewarm  liquids, 
because  in  cold  liquids  the  color-changes  take  place 
but  slowly. 

Aniline,  toluidine,  and  quinoline  are  alkaline  to- 
ward methyl  orange,  but  their  salts  are  neutral; 
hence  the  bases  may  be  titrated  by  its  means. 

Methyl  orange  may  be  advantageously  used  for 
determining  one  ingredient  in  a  substance,  after  a 
previous  titration  with  some  other  indicator  has 
been  made  of  another  substance  present.  For  in- 
stance, in  a  mixture  of  sodium  carbonate  and  sodi- 
um acetate,  the  former  may  be  estimated  by  means 
of  phenacetolin,  and  after  the  red  color  has  disap- 
peared, the  acetate  may  be  titrated  using  methyl 
orange.  Or,  soda  in  soap  may  be  first  titrated  by 
means  of  methyl  orange  and  sulphuric  acid,  and 
then  the  salt  present  in  the  same  solution  estimated 
by  adding  an  excess  of  potassium  chromate  and 
neutralizing  with  silver  nitrate.  Or,  again,  in  a 
mixture  of  alumina  and  soda,  or  in  caustic  soda 
containing  alumina,  the  sodium  may  be  estimated 
by  adding  phenolphtalein  to  the  solution,  heating, 
and  titrating  with  sulphuric  acid  until  the  red  color 
disappears,  then  adding  methyl  orange,  and  con- 
tinuing the  titration  of  the  warm  fluid  with  acid  to 
a  close. 

As  a  rule,  titrations  with  methyl  orange  are  best 
carried  on  at  the  ordinary  temperature. 


1 1 8  IN  DIG  A  TORS 


METHYL-ORANGE     AND      PHENOLPHTA- 
LEIN   SOLUTION 


ALKALiES=Red     NEUTRAL^  "    Acms^Pink 


Preparation  :  The  solution  is  prepared  by  dissolving 
10  parts  of  phenolphtalein  and  I  part  of  methyl 
orange  in  1000  parts  of  dilute  (50  per  cent.) 
alcohol. 

Application  :  The  mixture  of  methyl  orange  and 
phenolphtalein  was  recommended  by  Gawalowski 
as  an  excellent  neutrality  indicator.  The  neutral 
point  is  indicated  by  a  lemon-yellow  color.  The 
slightest  excess  of  either  acid  or  alkali  causes  a 
change  of  color,  the  acid  affording  a  deep  pink,  the 
alkali  a  fine  red. 

Five  to  ten  drops  of  the  solution  are  added  to  the 
liquid  to  be  titrated. 

METHYL  VIOLET 

2C«H4N(CH3)a.C6H4.N.C.CH3.HCl 

ALKALIES  =  Violet  ACIDS  =  Blue'  °*reen, 

or  Yellow 

Synonyms:  Gentian  Violet  36.  ;  Paris  Violet;  Direct 
Violet;  Methylaniline  Violet;  Dahlia;  Pyoktanin. 

Preparation  :  Methyl  violet  is  prepared  by  mixing  a 
saturated  aqueous  solution  of  3  parts  of  cupric 


METHYL    VIOLET 

nitrate,  3  parts  of  sodium  chloride,  and  I  part  of 
acetic  acid,  with  100  parts  of  clean,  washed  sand, 
then  adding  10  parts  of  pure  dimethylaniline,  and 
heating  the  mixture  at  a  temperature  of  140°  C.  for 
about  24  hours.  The  mass  obtained  is  then  com- 
minuted and  washed  with  a  solution  of  sodium 
sulphide,  which  dissolves  out  the -salts,  leaving  the 
sand,  copper  sulphide,  and  the  dye.  The  latter  is 
then  taken  up  by  water  acidulated  with,  hydro- 
chloric acid,  and  reprecipitated  by  salting  out  with 
sodium  chloride. 

Properties :  Methyl  violet  is  a  mixture  of  the  hydro- 
chlorates  of  penta-  and  hexa-methyl-pararosaniline, 
and  results  from  the  oxidation  of  the  dimethylani- 
line. It  occurs  as  a  green  powder  of  metallic 
luster,  and  is  soluble  in  alcohol,  amyl  alcohol,  and 
in  water.  Its  aqueous  solution  has  a  bright-violet 
color,  which  is  changed  by  acids,  according  to  their 
degree  of  concentration,  to  a  blue,  green,  or  even 
yellow,  color.  Alkalies  restore  the  violet  color. 
Acetic  acid,  and  other  very  weak  acids,  have  no 
effect  on  the  color. 

Application:  Methyl  violet  is  useful  for  determining 
the  quantity  of  sulphuric  or  other  strong  acid  present 
in  a  sophisticated  acetic  acid.  This  it  does  directly, 
because  it  is  unaffected  by  acetic  acid. 


I2O  INDICATORS 

ORANGE-PEEL  EXTRACT 

ALKALIES  =  Lemon-Yellow  ACIDS  =  Colorless 

Synonym-    Borntrager's  Indicator. 

Preparation ;  Orange-peel  extract  is  prepared  by 
macerating  I  part  of  fresh- cut  orange-peel  with  5 
parts  of  absolute  alcohol,  expressing,  shaking  with 
an  equal  volume  of  ether  to  remove  the  volatile  oil, 
and  then  separating  the  alcoholic  layer  for  use. 

Application  :  This  indicator  is  known  as  Borntrager's 
indicator.  One  part  of  the  extract  yields  with  100. 
parts  of. water  a  colorless  solution  which  is  colored 
a  lemon-yellow  by  alkalies,  the  color  being  again 
discharged  by  acids. 

The  indicator  is  unserviceable  in  the  presence  of 
free  ammonia.  Borntrager  states,  however,  that  in 
his  hands  it  has  given  closer  results  in  the  presence 
of  ammoniacal  salts  than  have  litmus,  corallin,  and 
phenolphtalein. 

PARA-NITROPHENOL 

C«H4.NO,.OH 

ALKALIES  =  Yellow  ACIDS  =  Colorless 

Synonym:  Nitrophenylic  Acid. 

Preparation:  Para-nitrophenol  is  prepared  by  the 
action  of  I  part  of  phenol  on  2  parts  of  nitric  acid 


PA  RA-NITROPHENOL  1 2 1 

diluted  with  4  parts  of  water,  and  separating  the 
para  product  from  the  accompanying  ortho  com- 
pound simultaneously  produced,  by  distilling  with 
steam.  The  ortho  compound  is  carried  over;  the 
para  compound  remains  behind  with  tarry  matters, 
and  is  purified  by  repeated  crystallization  from 
xylene. 

Properties :  Para-nitrophenol  forms  colorless  needles 
melting  at  about  112°  to  114°  C.,  and  readily  solu- 
ble in  alcohol,  but  only  slightly  so  in  water.  Its 
composition  is  CeH4(NO,).OH. 

Application  :  A  colorless,  I  :  10,000  aqueous  solu- 
tion of  para-nitrophenol  is  distinctly  colored  yellow 
by  a  trace  of  alkali,  and  hence  the  indicator  is 
sufficiently  sensitive  to  serve  in  I  :  5000  solution  for 
estimating  the  hardness  of  spring-  or  well-water. 
This  is  done  by  adding  5  Cc.  of  the  titrating  solu- 
to  100  Cc.  of  the  water,  and  to  100  Cc.  of  distilled 
water,  in  separate  beakers.  The  well-water  acquires 
a  more  or  less  deep-yellow  color,  according  to  its 
degree  of  hardness,  while  the  distilled  water  remains 
colorless.  To  the  latter,  normal  potassa  solution  is 
then  added  drop  by  drop  until  a  color  equal  in  depth 
to  that  acquired  by  the  well-water  is  developed. 
Each  Cc.  of  solution  added  will  represent  0.00028 
Gm.  of  CaO.  The  results  are  verified  by  adding 
normal  acetic-aci<d  solution  to  the  beaker  containing 
the  well-water.  The  quantity  of  normal  acid 


122  INDICATORS 

required  to  neutralize  the  potassa  solution  used 
should,  when  added  to  the  well-water  tested, 
be  sufficient  to  render  the  latter  colorless,  or 
almost  so. 

Para-nitrophenol  is  not  much  used  as  an  indi- 
cator, because  it  is  applicable  only  in  colorless  or 
faintly  colored  liquids. 

Its  sensitiveness  is  said  to  be  such  that  0.5  Cc.  of 
centinormal  alkali  solution  suffices  to  develop  the 
yellow  color  in  50  Cc.  of  the  liquid  to  be  titrated, 
and  to  which  some  of  the  indicator  had  been  added. 


PHENACETOLIN 

C16H12Oa 


ALKALIES  =  carb°nates  :  ACIDS  =  Yellow 

caustic:  Yellow 

Synonym  :     Degener's  Indicator. 

Preparation  :  Phenacetolin  is  obtained  by  heating 
equal  molecular  weights  of  concentrated  sulphuric, 
carbolic,  and  glacial  acetic  acids  in  a  vessel  pro- 
vided with  a  reflux  condenser,  the  product  being 
then  treated  with  water  until  all  free  acids  have 
been  washed  out  ;  the  residue,  phenacetolin,  is 
then  dried. 

Properties  :  Phenacetolin,  also  known  as  Degener's 
Indicator,  is  considered  to  be  identical  with  phena- 
cetein,  CI8H,,Oao  It  occurs  in  the  form  of  a 


PHENA  CE  TO  LIN  1 23 

yellowish-brown  powder,  slightly  soluble  in  water, 
but  soluble  in  alcohol,  yielding  a  green  solution. 
Application  :  Phenacetolin  may  be  used  in  the  form 
of  an  aqueous  I  1500  solution,  or  in  the  form  of  an 
alcoholic  I  :2OO  solution.  The  solutions  yield 
with  caustic  alkalies  a  pale  yellow,  scarely  percep- 
tible color,  but  with  carbonates  of  the  alkalies  and 
alkaline  earths,  as  well  as  with  sulphides  of  the 
alkalies  and  with  ammonia,  it  yields  intensely  red 
compounds,  all  but  those  of  the  alkaline  earths 
being  soluble,  and  affording  red  solutions.  Acids, 
even  organic,  color  the  solutions  yellow,  hence  in 
sodium  acetate  containing  sodium  carbonate  the 
latter  may  be  titrated  by  means  of  phenacetolin,  by 
using,  hydrochloric  or  sulphuric  acid  until  the  color 
changes  from  red  to  yellow,  then  adding  methyl 
orange,  and  finding  the  content  of  sodium  acetate 
by  titrating  until  the  red  color  reappears. 

Phenacetolin  is  very  useful  for  estimating  calcium 
hydrate  in  the  presence  of  calcium  carbonate,  cr 
sodium  hydrate  in  the  presence  of  sodium  carbonate, 
or  potassium  hydrate  in  the  presence  of  potassium 
carbonate,  when  the  caustic  alkali  is  present  in  not 
too  small  a  quantity ;  otherwise  the  color-change  is 
apt  to  be  very  uncertain.  For  carrying  out  the 
titration,  sulphuric  or  hydrochloric  acid  is  rapidly 
added  until  a  faint,  permanent  rose  color  is  apparent, 
which  will  indicate  the  caustic  alkali  or  lime  ;  further 
addition  of  acid  will  afford  a  red,  then  yellowish- 


1 24  JNDICA  TORS 

red,  and  finally  a  yellow  color  which  is  suddenly 
and  sharply  produced,  and  which  will  then  show 
the  quantity  of  carbonate  present. 

On  adding  a  dilute  acid  to  a  mixture  of  baryta 
and  barium  carbonate,  to  which  a  few  drops  of 
phenacetolin  solution  have  been  added,  the  color 
becomes  more  and  more  red  until  the  baryta  has 
been  saturated,  and  the  acid  begins  to  attack  the 
carbonate.  A  further  addition  of  acid  then  causes 
the  momentary  disappearance  of  the  color. 

The  indicator  cannot,  however,  be  used  in  mix- 
tures of  caustic  alkalies  and  their  carbonates  when 
ammonia  is  present. 

Bicarbonates  yield  a  red  color  with  phenacetolin. 

Sulphates,  nitrates,  and  chlorides  of  the  alkalies,  or 
of  the  alkaline  earths  (Ba,  Ca,  Mg.  and  Sr),  do  not 
affect  the  sensibility  of  the  indicator. 

Sulphites  are  prone  to  yield  mixed  colors,  but  the 
change  of  color  to  red  is  very  sharp  and  sudden, 
however,  when  the  point  of  saturation  is  complete. 

For  estimating  alkalies  with  oxalic  acid,  phenace- 
tolin is  useless.  It  is  also  useless  for  titrating  the 
ordinary  organic  acids.  With  arsenates,  the  change 
of  color  is  too  gradual  for  the  indicator  to  be  of 
service  ;  with  the  arsenites,  however,  the  color- 
changes  are  very  good,  and  accurate  results  are 
obtainable. 


PHENOL  NITROSYLSULPHONATE  12$ 

PHENOL   NITROSYLSULPHONATE 

ALKALIES  —  Blue  ACIDS  =  Red 

Synonym:   Lehman  and  Petri's  Dye. 

Preparation :  Phenol  nitrosylsulphonate  is  prepared 
by  mixing  5  Cc.  of  phenol  and  5  Cc.  of  concen- 
trated sulphuric  acid  while  keeping  the  mixture 
cold,  and  then  adding  20  Cc.  of  nitrosylsulphonic 
acid  (obtained  by  dissolving  5  Gm.  of  potassium 
sulphite  in  100  Gm.  of  cold  sulphuric  acid)  drop  by 
drop.  The  colorless  solution  is  then  heated  on  a 
water- bath  to  80°  C.  until  the  mass  acquires  a  dark 
bluish-violet  color.  The  mass  is  then  mixed  with 
2  liters  of  cold  water,  when  the  dye  separates  as  a 
dark-violet,  amorphous  substance.  This  is  sepa- 
rated by  filtration,  then  washed,  and  dried  at 
100°  C.  It  is  then  dissolved  in  ether,  and  finally 
obtained  in  a  condition  fit  for  use  as  an  indicator  by 
evaporating  the  ether. 

Properties:  Phenol  nitrosylsulphonate  occurs  as  a 
dark,  bluish-violet,  amorphous  solid  or  powder, 
soluble  in  acetone,  ether,  and  amyl-,  ethyl-,  or  me- 
thyl-alcohol, affording  yellow  solutions;  slightly 
soluble  in  chloroform,  difficultly  so  in  benzene  and 
toluene,  and  insoluble  in  benzin. 

Application :  Phenol  nitrosylsulphonate  was  recom- 
mended as  an  indicator  by  Theodor  Lehman  and 
Julius  Petri.  These  authors  claim  it  to  possess 


126  INDICATORS 

properties  like  those  of  litmus,  while  being  much 
more  sensitive  than  phenolphtalein,  and  that  it  is 
therefore  well  adapted  for  use  in  titrimetry.  Com- 
pared with  phenolphtalein,  its  sensitiveness  is  such 
that  whereas  when  phenolphtalein  is  added  to  50  Cc. 
of  recently  boiled,  distilled  water,  0.5  Cc.  of  centi- 
normal  caustic  alkali  are  required  to  show  a  distinct 
red,  while,  when  2  drops  of  an  alcoholic  phenol- 
nitrosylsulphonate  solution  are  added  to  50  Cc.  of 
recently  boiled,  distilled  water,  the  latter  is  colored 
distinctly  blue  by  2  drops  of  centinormal  caustic 
alkali. 

The  indicator  yields  a  blue  color  with  alkalies, 
and  a  red  with  acids.  Like  litmus,  it  is  affected  by 
carbonic-acid  gas;  it  is  also  unserviceable  for  am- 
monia. It  gives  very  good  results,  however,  with 
alkalies,  alkaline  earths,  mineral  acids,  and  oxalic, 
acetic,  and  formic  acids. 


PHENOLPHTALEIN 


ALKALIES  =  Red  ACIDS  =  Colorless 

Synonym  :    Dioxyphtalophenone  ;    Luck's  Indicator. 

Preparation  :  Phenolphtalein  is  prepared  by  heating 
together  5  parts  of  phtalic  anhydride  (C8H4Ot),  10 
parts  of  phenol,  and  4  parts  of  concentrated  sul- 
phuric acid  for  several  hours  at  a  temperature 


PHENOLPHTA  LEIN 

between  120°  and  130°  C.  The  resulting  red  mass 
is  then  boiled  with  water,  and  the  resinous  residue, 
consisting  of  impure  phenolphtalein,  is  filtered  off, 
and  dissolved  in  dilute  soda  lye.  The  solution  is 
filtered  and  precipitated  by  neutralizing  with  acid, 
the  precipitate  being  finally  purified  by  recrystal- 
lizing  from  alcohol. 

Properties:  Phenolphtalein  occurs  as  a  nearly  white 
or  yellowish-white,  crystalline  powder,  nearly  in- 
soluble in  water,  but  soluble  in  10  parts  of  alcohol, 
and  in  dilute  alcohol.  It  melts  at  250  C.  Its 
composition  is  CJOHMO4. 

Tests  :  It  is  very  important  that  the  purity  of  phe- 
nolphtalein be  assured,  because  on  this  depends  the 
sensitiveness  of  the  indicator.  Many  samples  are 
likely  to  contain  impurities  in  the  form  of  some  of 
the  resinous  substance  produced  during  their  manu- 
facture. A  good  article  should  respond  to  the  fol- 
lowing tests : 

0.5  Gm.  of  phenolphtalein  heated  on  platinum 
foil  should  leave  no  residue ;  it  should  yield  a  clear 
solution  with  10  parts  of  alcohol,  and  a  I  :ioo  solu- 
tion in  alcohol  should  be  colorless.  Its  sensitiveness 
should  be  such  that  not  more  than  0.08  to  0.09  Cc. 
of  decinormal  alkali  should  be  required  to  produce 
a  violet  (not  red)  color  in  250  Cc.  of  recently  boiled 
and  cooled  distilled  water  to  which  a  few  drops  of 
phenolphtalein  solution  have  been  added.  To  pro- 


128  INDICATORS 

duce  a  distinct  redness,  0.5  Cc.  of  centinormal 
potassa  solution  are  required  when  0.5  Cc.  of  phe- 
nolphtalein  solution  are  added  to  100  Cc.  of  dis- 
tilled water. 

Application  :  Phenolphtalein  was  recommended  as  an 
indicator  by  Luck,  and,  after  litmus  and  methyl 
orange,  is  the  one  most  favored.  It  is  exceedingly 
sensitive,  and  changes  very  sharply  and  suddenly 
from  a  fine  red  with  fixed  alkalies,  to  a  colorless 
solution  with  acids  (even  carbonic),  and  vice  versa. 
Its  sensitiveness  is  such  that,  as  Luck  states,  the 
slightest  trace  of  alkali,  even  in  highly  dilute  solu- 
tion (i  :  100,000),  gives  a  distinct  color.  It  pos- 
sesses the  properties  of  a  very  weak  acid. 

Solution  of  phenolphtalein  for  use  is  made  by 
dissolving  I  Gm.  of  phenolphtalein  in  100  Cc.  of 
50$  alcohol.  But,  in  view  of  the  slight  acid  prop- 
erties of  the  indicator,  the  solution  must  be  ren- 
dered neutral  by  cautiously  adding  a  few  drops  of 
centinormal  alkali  until  very  faint  redness,  and  then 
adding  a  drop  of  centinormal  acid.  About  5  drops 
of  the  solution  are  added  to  100  Cc.  of  the  solution 
to  be  titrated. 

Salts  of  the  fixed  alkalies  have  no  influence  on  the 
delicacy  of  the  reaction,  but  the  ammonium  salts 
have,  most  probably  from  the  action  of  the  am- 
monia on  the  phenolphtalein,  resulting  in  the 
formation  of  phenol  di-imidophtalein,  which  yields 


PHENOLPHTA  LEIN  1 29 

colorless  solutions  with  alkalies.      The  reaction   oc- 
curring may  be  expressed  as  follows : 

G»H,.0.  +  2NH,  =  C..H..N  ,O.  +  2H,O. 

phenolphtalein  phenol  di-imidophtalein 

The  indicator  is,  hence,  useless  for  ammonia. 
Phenolphtalein  is,  however,  one  of  the  best  indi- 
cators for  titrating  caustic  alkalies  and  their  carbon- 
ates, and  for  the  alkali  earths.  By  its  means  also, 
caustic  alkalies  may  be  titrated  in  the  presence  of 
carbonates  or  bicarbonates,  and  carbonates  may  be 
estimated  in  the  presence  of  bicarbonates,  which 
are  neutral  to  the  indicator,  and  the  solution 
becomes  colorless  as  soon  as  the  alkali  or  carbonate 
has  been  neutralized.  The  indicator  is  very 
sensitive  to  carbonic  acid,  however,  hence  the 
estimations  must  be  conducted  in  boiling  solutions.* 
The  residual  bicarbonate  may  then  be  estimated,  if 
desired,  with  methyl  orange.  Caustic  alkali  in  the 
presence  of  carbonate  may  also  be  estimated  by  first 
diluting  the  solution  so  that  not  more  than  about 
0.5$  of  total  alkali  is  present,  then  precipitating  the 
carbonate  with  barium  chloride  in  excess,  and 
rapidly  titrating  to  avoid  the  formation  of  new 
carbonate  from  the  caustic  alkali  in  the  solution. 
The  solution  containing  the  precipitated  barium 
carbonate  need  not  be  filtered,  as  the  salt  does  not 
interfere  with  the  reaction. 

Phenolphtalein   may  be   used   for  titrating  alkali 


1 3°  INDICA  TORS 

sulphides.  These  yield  a  red  color  with  the  in- 
dicator, which  is  discharged  when  half  the  alkali 
has  been  converted  into  sodium-  (or  potassium-) 
hydrogen  sulphide.  The  total  alkali  may  also  be 
titrated,  but  in  this  case  the  operation  must  be 
effected  in  boiling  solutions,  since  the  liberated 
hydrogen  sulphide  destroys  the  color  of  the  solu- 
tion. 

The  alkali  radical  of  borax  cannot  be  estimated 
with  phenolphtalein,  because  the  color  produced  on 
adding  acid  fades  away.  The  boric  acid  in  borax 
may  be  titrated  accurately,  however,  by  employing  a 
»/5  sodium-hydrate  solution,  but  it  is  necessary 
to  first  add  about  30$  of  glycerin  to  the  liquid  to 
be  titrated. 

Normal  sulphites  are  neutral  to  phenolphtalein,  in 
both  hot  and  cold  solutions.  Reddened  phenol- 
phtalein solutions  are  decolorized  by  boric  and 
arsenous  acids,  potassium  bichromate  and  gum  arabic. 
For  arsenites  the  indicator  is  not  very  serviceable, 
as  it  only  shows  about  90^  of  the  combined  sodium 
or  potassium.  With  the  arsenates,  however,  a  well- 
defined  change  occurs  when  one-third  of  the  alkali  is 
neutralized.  With  the  bibasic  phosphates,  which  are 
almost,  but  not  quite,  neutral  to  the  indicator,  the 
results  are  not  very  satisfactory. 

Codeine,  morphine,  cinchonine,  quinine,  quinidine, 
brucine,  strychnine,  aniline,  quinoline,  and  paratolui- 
dine  are  neutral  to  phenolphtalein,  and  may  be 


PHENOLPHTA  LEIN  1 3  I 

readily  titrated  by  its  means,  their  salts  being  dis- 
solved or  suspended  in  a  few  Cc.  of  alcohol  and 
then  titrated  with  alkali  to  redness.  The  acid 
radicals  of  all  the  alkaloids  excepting  coniine, 
nicotine,  and  codeine,  may  also  be  estimated. 

Phenolphtalein  is  excellent  for  estimating  the 
organic  acids,  such  as  oxalic,  acetic,  tartaric,  citric, 
lactic,  etc.,  and  particularly  in  mixtures  of  alcohol 
and  ether,  in  which  many  organic  acids  which  are 
insoluble  in  water  may  be  readily  titrated.  It  is 
best  to  titrate  the  organic  acids  in  cold  or  only 
moderately  warm  solutions  when  using  potassium- 
or  sodium  hydrate  as  a  titrating  fluid.  The  indi- 
cator is  also  exceedingly  useful  for  titrating  fatty 
acids  in  alcoholic  solution,  and  for  free  alkali  in 
soap  where  litmus  is  inapplicable. 

The  indicator  can  be  used  with  only  those  metals 
that  yield  white  precipitates  with  sodium  sulphide  or 
with  a  carbonate  of  an  alkali.  •  It  is  also  useful  in 
many  cases  where  the  solutions  to  be  titrated  are 
colbred,  because  in  these  the  color-changes  may  be 
quite  readily  observed. 

It  has 'been  pointed  out  by  Messrs.  N.  and  C. 
Draper  that  the  color  of  phenolphtalein  solutions 
colored  red  by  potassa  or  soda  is  partially  discharged 
on  the  addition  of  alcohol,  the  reason  ascribed 
being  the  formation  of  some  bicarbonate  by  taking 
up  carbonic  acid  from  the  air.  On  heating,  or  on 
dilution  with  water,  the  color  is  restored. 


I 3  2  JND  1C  A  TO  AS 

Phenolphtalein  is  also  used   in  the  form  of  test- 
paper  (see  Test-papers). 


PHENYLENE    DIAMINE,    META- 

C,H4(NHa)a 
Synonym  :     Meta-diamido  Benzene. 

Preparation :  Meta-phenylene-diamine  is  obtained 
by  the  reduction  of  dinitrobenzene,  or  nitraniline, 
with  tin  and  hydrochloric  acid. 

Properties  :  The  meta-phenylene  diamine  occurs  as 
a  crystalline  powder  or  mass,  readily  soluble  in  alco- 
hol and  in  ether,  and  but  little  so  in  water.  It  is  a 
strong  di-acid  base,  and  capable  of  forming  well- 
defined  salts  with  acids. 

Tests  :  Meta-phenylene  diamine  is  readily  prone  to 
change  on  contact  with  air,  when  it  loses  its  origi- 
nally white  color  and  becomes  reddish.  A  I  :  20 
aqueous  solution  should  be  colorless,  or  only  faintly 
yellow  ;  if  the  color  is  deeper,  the  preparation 
should  be  rejected.  On  account  of  its  readiness  to 
decompose,  the  preparation  must  be  kept  in  small, 
well-closed  bottles. 

Application  :  Meta-phenylene  diamine,  as  well  as  its 
hydrochloride,  C6H4(NH3)3.2HC1,  which  occurs  as 
a  white  or  faintly  reddish-white  crystalline  powder 
soluble  in  water,  is  very  useful  for  detecting  nitrites 
in  potable  water.  On  adding  sulphuric  acid  to  the 


PHYLLOCYANIN  133 

suspected  water,  the  nitrous  acid  liberated  from  any 
nitrites  that  may  be  present  affords  a  yellow  color 
even  if  the  slightest  traces  of  nitrites  are  present.  For 
this  purpose  a  I  :  200  aqueous  solution  of  the  base 
or  its  salt  is  used.  I  Cc.  of  the  solution  is  added  to 
IOO  Cc.  of  the  suspected  water,  and  I  Cc.  of  diluted 
sulphuric  acid  (1:3)  added.  The  color  so  obtained 
is  then  compared  with  a  known  standard,  by  which 
means  the  quantity  of  nitrites  present  may  be  esti- 
mated. 

Meta-phenylene  diamine  hydrochloride  gives  also 
an  exceedingly  sharp  reaction  with  aldehydes,  and  is 
used  for  detecting  the  latter  in  alcohol. 


PHYLLOCYANIN 

ALKALIES  —  Green,  then   Yellow,  and   finally  almost 
Black 

Synonyms  :  Pellagri's  Indicator  ;  Phyllocyanic 
Acid. 

Source  :  Phyllocyanin  was  discovered  (and  named) 
by  Fr£my,  as  being  one  of  the  two  constituents 
(Filhol,  and  also  Stokes,  claim  there  are  four)  to 
which  chlorophyll  owes,  in  part,  its  color.  Fremy 
separated  it  from  the  accompanying  yello<v  phyllo- 
xanthin,  also  named  by  him,  by  shaking  chlorophyll 
with  a  mixture  of  two  parts  of  ether  and  one  part 
of  dilute  hydrochloric  acid.  The  latter  dissolves 


I  34  1NDICA  TORS 

the  phyllocyanin,  and  the  former  dissolves  the 
phylloxanthin.  The  immiscible  solvents  were  then 
separated. 

Preparation  :  Phyllocyanin  is  prepared  by  Fremy's 
process,  or  by  boiling  chlorophyll  with  a  strong 
alcoholic  solution  of  potassium  hydroxide,  neutraliz- 
ing the  solution  with  hydrochloric  acid,  and  then 
filtering.  On  evaporating  the  filtrate  the  phyllo- 
cyanin is  obtained. 

Properties  :  Phyllocyanin  occurs  as  a  dark  blue  mass 
soluble  in  water  and  alcohol,  the  solutions  having 
an  olive  color  with  bronze-red  or  violet  reflection. 
It  is  acid  in  character,  and  yields  brown  or  green 
salts,  those  of  the  alkalies  being  soluble  in  water. 
With  sulphuric  and  hydrochloric  acids  it  yields  solu- 
tions which  are  green,  reddish,  violet,  or  a  hand- 
some blue,  according  to  the  strength  of  the  solu- 
tions. 

Application  :  For  use  a  solution  of  phyllocyanin  is 
prepared  to  which  just  sufficient  acid  is  added  to 
change  the  color  of  the  solution  to  a  purple. 

The  indicator  is  quite  sensitive  to  alkalies,  which 
change  the  color  of  the  acid  solution  to  green,  then 
yellow,  and  finally  almost  black. 


POIRRIER  BLUE  135 

POIRRIER  BLUE,  C4B 

.  carbonates :   Blue  .  -.. 

ALKALIES  =  caustic .         Red  ACIDS  =  Blue 

Preparation  :  Poirrier  Blue,  €46,  is  obtained  by  the 
action  of  sulphuric  acid  on  triphenylrosaniline,  and 
is  closely  allied  to  Gentian  Blue  in  properties. 

Properties :  Poirrier  Blue,  €46,  occurs  as  a  blue 
powder  having  a  coppery  luster.  It  is  soluble  in 
water  and  in  alcohol,  yielding  blue  solutions.  That 
obtained  with  alcohol  is  lighter  in  color  than  the 
aqueous  solution,  but  the  color  is  deepened  on  the 
addition  of  water.  Potassium  and  sodium  hydrates 
change  the  color  to  a  red,  the  blue  being  restored 
on  adding  an  acid.  Ammonia,  however,  decolorizes 
the  solution,  but  the  blue  is  also  restored  in  this 
case  by  an  acid. 

Application  :  Poirrier  Blue,  €46,  was  first  recom- 
mended as  an  indicator  by  Engel  and  Ville.  An 
aqueous  I  :  500  solution  of  the  indicator  is  employed, 
of  which  one  or  two  drops  are  added  to  100  Cc.  of 

.  the  liquid  to  be  titrated.  In  the  presence  of  only 
alkali  carbonates  the  color  remains  blue,  but  if  caustic 
bases  are  present,  the  color  changes  to  red.  Ammonia, 
ethylamine,  and  other  amines  do  not  change  the 
color.  The  indicator  is  exceedingly  sensitive  to 
acids,  and  the  results  obtained  by  its  means  are 
very  good,  compared  with  those  obtained  with 


136  INDICATORS 

litmus  or  methyl  orange.  Borax  and  boric  acid 
sharply  change  the  color  to  blue,  the  solutions  only 
becoming  red  when  the  total  acid  has  been  com- 
pletely neutralized.  Phosphates  and  arsenates  act 
similarly.  This  is  a  valuable  property  peculiar  to 
the  Poirrier  Blue;  many  indicators  are  affected  by 
alkalies  before  neutralization  is  complete.  Bicar- 
bonates  of  the  alkalies  afford  a  blue  color  which  does 
not  change  until  the  bicarbonates  have  been  con- 
verted into  basic  carbonates. 

Morphine,  phenols,  resorcin,  chloral,  and  hydrocy- 
anic acid,  act  like  acids  towards  the  indicator,  and 
may  be  titrated  by  its  means.  Phosphoric  and 
arsenic  acids  are  tribasic  with  the  Blue,  but  as  the 
tribasic  phosphates  are  very  unstable,  and  the 
change  of  color  is  not  very  marked  in  consequence, 
the  indicator  is  unserviceable  for  titrating  them. 
Carbolic  acid  is  monovalent,  and  resorcin  is  bivalent 
with  the  Blue ;  monovalent  alcohols  are  neutral,  and 
polyvalent  alcohols  are  acid.  The  aldehydes  are  all 
neutral. 

Poirrier  Blue  has  the  character  of  a  very  weak 
acid,  and  its  salts  are  so  unstable  that  they  are  de- 
composed by  water  alone  when  in  very  great  dilu- 
tion, hence  readings  with  the  indicator  may  be 
misleading  unless  sufficient  of  the  indicator  is  present. 
The  change  of  color  in  the  latter  case  is  very  sharp, 
and  is  facilitated  if  a  little  alcohol  is  added  to  the 
solution  to  be  titrated. 


POLYSULPHIDE   SOLUTION  137 

POLYSULPHIDE    SOLUTION 

ALKALIES  =  No  Precipitate  ACIDS  =  Turbidity 

Synonym  .     Bolton's  Indicator. 

Preparation :  The  polysulphide  indicator  is  a  very 
concentrated  solution  of  sublimed  sulphur  in  a  solu- 
tion of  an  alkaline  sulphide.  The  solution  must  be 
concentrated  in  order  to  avoid  the  necessity  of  using 
too  large  a  quantity  of  the  indicator,  which  would 
vitiate  the  results  because  of  the  natural  alkalinity  of 
the  solution ;  while  at  the  same  time  sufficient  dis- 
solved sulphur  must  be  present  to  afford  a  clearly 
visible  precipitate  on  neutralization. 

Application  :  The  polysulphide  solution  was  recom- 
mended as  an  indicator  by  Bolton.  Its  action  de- 
pends on  the  fact  that  sulphur  is  precipitated  in 
neutral  or  acid  solutions,  but  is  soluble  in  alka- 
line sulphide  solutions.  For  the  application  of 
the  indicator  a  drop  or  two  of  the  solution  is  a  suf- 
ficient addition  to  250  Cc.  of  the  liquid  to  be, 
titrated.  .  The  liquid  is  then  heated,  the  titration 
being  best  effected  in  an  Erlenmeyer  flask,  and 
when  it  boils,  the  titrating  acid  is  permitted  to  flow 
in.  So  long  as  the  liquid  remains  alkaline,  the 
liberated  sulphur  redissplves,  but  on  the  least  ex- 
cess of  acid,  the  sulphur  renders  the  liquid  milky. 
Of  course  the  indicator  can  only  be  used  in  alkaline 
solutions.  The  natural  alkalinity  of  the  polysul- 


138  INDICATORS 

phide  solution  may  be  determined  beforehand,  and 
the  necessary  corrections  in  the  acid-readings  be 
made. 


POTASSIUM    BICHROMATE 

K2Cr207 
ALKALIES  —  Reddish-Yellow     ACIDS  =  Pale-  Yellow 

Synonyms  :  Potassium  Bichromate  ;  Acid  Potassium 
Chromate;  Red  Potassium  Chromate  ;  Potassium 
Anhydrochromate  ;  Richter's  Indicator. 

Preparation  :  A  mixture  of  finely  powdered  chrome 
ironstone  (FeOCr3O3),  caustic  lime,  and  potassium 
carbonate  is  heated  for  several  hours.  Oxidation  en- 
sues, carbon  dioxide,  potassium  chromate,  calcium 
chromate,  and  iron  oxide  resulting  as  follows: 


2FeOCraO,  +  3K,CO,  +  CaO  +  ;O 

=  3KaCr04  +  CaCr04  +  Fe,O3  +  3CO3. 

The  greenish-yellow  mass  so  obtained  is  exhausted 
with  a  little  boiling  water  which  dissolves  out  the 
soluble  chromates.  The  calcium  salt  is  then  de- 
composed by  potassium  hydroxide,  and  the  potas- 
sium chromate  in  solution  converted  into  a  bichro- 
mate by  the  addition  of  sufficient  sulphuric  acid. 

The    salt    is    then    crystallized,   and    purified    by 
recrystallization. 

Properties  :    Potassium   bichromate   occurs    as  large, 


POTASSIUM  BICHROMATE  139 

orange-red,  translucent  crystals  having  a  bitter,  me- 
tallic taste,  and  soluble  in  10  parts  of  water  at 
15°  C.  Its  formula  is  K2CraO7. 

Tests  :  Potassium  bichromate  should  be  tested  for 
sulphuric  acid  by  dissolving  3  Gm.  in  100  Cc.  of 
distilled  water,  and  adding  hydrochloric  acid  and 
barium-chloride  solution.  No  change  or  precipitate 
should  be  observed  within  12  hours.  Too  little 
hydrochloric  acid  should  be  guarded  against,  other- 
wise a  misleading  precipitate  of  barium  chromate 
may  be  formed. 

It  is  important  that  the  salt  be  tested  for  any 
sulphuric  acid  that  might  be  present,  when  intended 
for  use  as  an  oxidizer.  Fresenius  tests  it  by  adding 
hydrochloric  acid  and  alcohol,  and  after  complete 
reduction,  adding  the  barium  chloride  and  per- 
mitting the  mixture  to  stand  for  12  hours. 

The  salt  is  tested  for  chlorides  by  adding  some 
nitric  acid,  warming  the  solution,  and  then  adding  a 
few  drops  of  silver-nitrate  solution.  No  precipi- 
tate should  'be  formed.  Calcium  salts  may  be 
detected  by  adding  I  Cc.  of  ammonia  water  to  10 
Cc.  of  a  I  :  20  aqueous  solution  of  the  salt,  and  then 
adding  a  little  ammonium-oxalate  solution.  No 
precipitate  should  be  formed. 

Application  :  Potassium  bichromate  was  recommend- 
ed as  an  indicator  by  M.  Richter.  The  bichromate 
is  dissolved  in  water,  a  very  little  phenolphtaiein 


140  INDICATORS 

is  added,  and  potassium-hydrate  solution  added 
cautiously  until  a  very  faint  yellowish-red  solution 
results.  The  change  of  color  from  a  pale-yellow 
with  acids  to  a  reddish-yellow  with  alkalies  is  very 
sharp.  The  indicator  is  useful  for  titrating  caustic 
alkalies  and  ammonia,  the  formation  of  monochro- 
mates  being  readily  observed. 

POTASSIUM    CHROMATE 

KaCrO4 

SILVER  SALTS  =  Red 

Synonyms:  Potassium  Monochromate;  Neutral  Po- 
tassium Chromate;  Yellow  Potassium  Chromate. 

Preparation  :  Potassium  chromate  is  obtained  by  a 
process  exactly  similar  to  that  described  in  the 
preparation  of  potassium  bichromate,  only  the  final 
conversion  into  a  bichromate  is  omitted,  the  yellow 
liquid  being  filtered,  concentrated  by  evaporation, 
and  set  aside  to  crystallize.  The  crystals  are  then 
purified  by  recrystallization. 

The  chromate  is  also  obtained  by  passing  chlorine 
gas  into  a  hot  solution  of  caustic  potassa  containing 
chromium  hydroxide  in  suspension. 

A  pure,  chlorine-free  preparation  is  secured  by 
fusing  25  parts  of  potassium  bichromate  with  20 
parts  of  pure  potassium  nitrate  (or  a  corresponding 
quantity  of  potassium  carbonate).  This  yields  34 
parts  of  pure  neutral  potassium  chromate. 


POTASSIUM   CHROMATE  14! 

Properties  :  Potassium  chromate  occurs  as  yellow, 
translucent  crystals,  permanent  in  air,  and  soluble 
in  2.7  parts  of  water  at  15.5°  C.  and  in  1.57  parts  at 
100°  C.  It  is  insoluble  in  alcohol. 

On  adding  an  acid  to  the  solution  of  the  salt,  the 
yellow  color  is  changed  to  red,  due  to  the  formation 
of  a  bichromate.- 

Solutions  of  the  salt  are  faintly  alkaline  towards 
litmus  arid  curcuma,  but  are  neutral,  according  to 
De  Vrij,  to  phenolphtalein. 

Tests :  Potassium  chromate  should  be  tested  for  free 
alkali  by  dissolving  o.  I  Gm.  of  the  salt  in  25  Cc.  of 
water,  and  adding  a  few  drops  of  phenolphtalein 
solution. 

Sulphates  and  chlorides  are  tested  for  as  described 
under  potassium  bichromate. 

Alumina  and  alkaline  earths  are  tested  for  by 
adding  ammonia  and  ammonium  oxalate  to  a  1 : 20 
solution  of  the  chromate ;  there  should  be  no  pre- 
cipitate. 

Application  :  Potassium  chromate  is  used  as  an  in- 
dicator in  the  titration  of  halogen  salts,  using  silver- 
nitrate  solution  as  a  titrating  fluid.  The  moment 
when  all  the  halogen  radical  of  the  salt  has  combined 
with  the  silver  is  indicated  by  a  red  precipitate  or 
color,  due  to  the  formation  of  silver  chromate. 

It  has  also  been  employed  in  the  estimation  of 
quinine. 


142  INDICA  TORS 

For  use  a  solution  of  I  Gm.  in  10  Cc.  of  distilled 
water  is  prepared. 

POTASSIUM  FERRICYANIDE 

K8FeaCyia 

FERROUS  SALTS  =  Blue      FERRIC  SALTS  =  Colorless 

Synonyms  :  Red  Prussiate  of  Potash  ;  Potassium 
Ferridcyanide ;  Potassio-ferric  Cyanide, 

Preparation  :  Potassium  ferricyanide  'is  prepared  by 
passing  chlorine  gas  into  a  I  :  8  solution  of  potas- 
sium ferrocyanide  until  a  small  sample  of  the  solu- 
tion no  longer  gives  a  blue  reaction  with  ferric 
chloride. 

Reichard  proposes  bromine  as  a  substitute  for 
chlorine  gas,  and  states  that  I  part  of  bromine  suf- 
fices for  5  parts  of  potassium  ferrocyanide. 

Properties :  Potassium  ferricyanide  occurs  as  red 
crystals  soluble  in  4  parts  of  cold  water  and  yield- 
ing a  brownish-yellow  solution.  The  dilute  solution 
is  lemon-yellow.  The  salt  is  but  slightly  soluble  in 
alcohol. 

Tests  :  Potassium  ferricyanide  should  be  tested  for 
sulphuric  acid  by  adding  to  a  I  :  20  solution  a  little 
hydrochloric  acid  followed  by  barium-chloride  solu- 
tion. Any  ferrocyanide  present  may  be  detected 
by  adding  a  little  ferric-chloride  solution,  which 
would  give  a  blue  color. 

Chlorides  may  be  detected   by  fusing  0.5  Gm.    of 


POTASSIUM  FERRICYANIDE  143 

the  permanganate  with  I  Gm.  of  pure  potassium  ni- 
trate, exhausting  the  fused  mass  with  water,  filtering, 
acidulating  the  filtrate  with  nitric  acid,  and  then 
adding  silver-nitrate  solution. 

Sodium  salts  are  detected  by  dissolving  I  Gm.  of 
the  permanganate  in  water,  acidulating  with  hydro- 
chloric acid,  adding  ferric  chloride  in  excess  to  pre- 
cipitate the  excess  of  iron,  filtering,  and  then 
testing  the  filtrate  with  potassium  metantimoniate. 

Application:  Potassium  ferricyanide  is  employed  as  an 
indicator  in  the  titration  of  ferrous  salts  by  means 
of  potassium  bichromate.  The  latter  oxidizes  the 
ferrous  salts  to  ferric,  the  end  of  the  reaction  being 
known  when  a  blue  color  ceases  to  be  yielded,  on 
adding  the  bichromate  solution.  The  process  does 
not  yield  very  satisfactory  results,  because  the  indi- 
cator cannot  be  added  directly  to  the  ferrous-salt 
solution,  but  a  drop  or  two  of  the  latter,  after  every 
addition  of  bichromate,  is  brought  into  contact  with 
the  indicator  solution  on  a  porcelain  tile.  The 
method  is  thus  very  troublesome,  and  takes  up  too 
much  time. 

The  ferricyanide  is  also  used  in  the  volumetric 
gas  analysis  of  hydrogen  dioxide,  and  also  for 
alkalies,  and  alkali  earths.  It  is,  besides,  used  in 
estimating  phosphoric  acid  by  means  of  uranium 
acetate. 

For  use  a  recently  prepared  I  :  10  solution  is 
prepared. 


144  INDICA  TORS 

* 

POTASSIUM  HYDRORUFIGALLATE  (?) 
ALKALIES  =  Carmine-red  ACIDS  =Yellow 

Synonym  :     Oser  and  Kalmann's  Indicator. 

Preparation  :  On  treating  gallic  acid  with  potassium 
permanganate,  hydrorufigallic  (tetrahydroellagic) 
acid,  C14H10O8',  is  obtained  in  the  form  of  yellow 
needles  readily  soluble  in  alcohol  and  in  ether,  but 
difficultly  soluble  in  water.  It  has  been  found, 
however,  that  a  sensitive  indicator  may  be  obtained 
by  fusing  I  part  of  the  hydrorufigallic  acid  so  ob- 
tained with  5  parts  of  caustic  potassa,  until  a 
reddish-violet  mass  results,  an  isomeric  compound 
being  thus  formed,  and  which,  when  decomposed 
by  sulphuric  acid,  affords  a  greenish-yellow  residue. 
This  is  finally  purified  by  recrystallization  from  boil- 
ing water. 

Properties  :  The  preparation  obtained  as  above  oc- 
curs as  greenish-yellow,  microscopic  crystals,  which 
sublime  at  200°  to  220°  C.,  decompose  above  230° 
C.,  and  dissolve  in  solutions  of  caustic  alkalies  and 
yield  a  green  solution,  the  color  of  which  changes 
to  a  carmine-red  on  contact  with  air.  The  red  color 
is  changed  to  yellow  by  acids,  and  restored  again 
by  alkalies. 

Application  :  The  indicator  is  useful  in  titrating 
mineral  waters,  because  it  is  reddened  by  carbonates 


POTASSIUM  PERMANGANATE  145 

of  the  alkalies,  magnesium,  calcium,  and  iron,  but 
is  unaffected  by  carbonic-acid  gas.  The  combined 
carbonic  acid  in  well-water,  springs,  etc.,  is  also 
readily  determined  by  its  means. 


POTASSIUM  PERMANGANATE 

KMn04 

REDUCERS  AND  ORGANIC  MATTER  =  Decolorization 

Synonyms  :  Potassium  Hypermanganate  ;  Potassium 
Oxymanganate ;  Potassium  Supermanganate. 

Preparation :  Potassium  permanganate  is  prepared 
by  heating  10  parts  of  caustic  potassa,  7  parts  of 
potassium  chlorate,  and  8  parts  manganese  dioxide 
in  a  crucible  until  a  test  taken  from  the  mass  dis- 
solves and  yields  a  deep-green  solution.  The  mass 
is  then  boiled  with  water  until  the  potassium  man- 
ganate  has  become  converted  in  a  permanganate, 
evidenced  by  a  change  of  color  from  green  to  red. 
The  solution  is  then  concentrated  by  evaporation, 
and  set  aside  to  crystallize. 

According  to  an  improved  process  proposed  by 
Boettger,  2  parts  of  caustic  potassa  and  I  part  of 
potassium  chlorate  are  fused  together,  and  then  2 
parts  of  finely  powdered  manganese  dioxide  care- 
fully added,  the  heat  being  continued  for  a  short 
time.  The  fused  mass  is  then  comminuted  and 
boiled  with  40  parts  of  water,  while  a  stream  of  car- 


146  INDICATORS 

bon  dioxide  is  forced  through  the  liquid  until  a  few 
drops  of  the  latter  placed  on  white  paper  no  longer 
show  a  green,  but  red,  color.  The  solution  is  then 
concentrated  and  allowed  to  crystallize.  Instead 
of  carbon  dioxide,  chlorine  gas  and  bromine  have 
also  been  used,  and  with  good  results. 
Properties:  Potassium  permanganate  occurs  as  dark- 
violet,  anhydrous  crystals  presenting  a  metallic  lus- 
ter. It  is  soluble  in  16  parts  of  water  at  15°  C., 
yielding  neutral  solutions  having  a  deep-purple 
color. 

Potassium  permanganate  is  an  exceedingly  pow- 
erful oxidizer,  and  is  readily  reduced  by  all  organic 
matter;  hence,  it  must  not  be  carelessly  brought 
into  contact  with  readily  oxidizable  substances.  On 
being  heated  it  yields  10.5$  oxygen. 

Its  solutions  are  decomposed  by  mineral  acids 
and  by  alkalies,  manganous  salts  resulting  with  the 
former  and  manganates  with  the  latter. 

Carbonates  of  the  alkalies  are  indifferent  toward 
potassium  permanganate,  but  ammonia  decomposes 
and  decolorizes  it.  The  dry  salt,  treated  with  con- 
centrated sulphuric  acid,  yields  ozone. 

Tests :  Sulphates  and  chlorides  when  present  may  be 
detected  by  boiling  0.5  Gm.  of  the  salt  with  2  Cc. 
of  alcohol  and  25  Cc.  of  distilled  water,  and  acidu- 
lating the  colorless  solution  with  nitric  acid.  On 
now  adding  barium  nitrate  or  silver  nitrate,  white 
precipitates  will  form. 


REFLECTING    GALVANOMETER  H7 

Nitrates  are  tested  for  by  dissolving  0.5  Gm.  of 
the  permanganate  in  5  Cc.  of  hot  water,  and  grad- 
ually adding  oxalic  acid  until  decolorization  is 
complete.  2  Cc.  of  the  filtrate  are  then  mixed 
with  2  Cc.  of  concentrated  sulphuric  acid,  and 
the  mixture  overlaid  on  I  Cc.  of  a  concentrated 
ferrous-sulphate  solution.  If  a  nitrate  is  present,  a 
brown  zone  will  form  at  the  point  of  contact  of  the 
two  liquids. 

Application  :  Potassium  permanganate  is  not  used 
as  an  indicator  per  se.  It  does,  however,  indicate 
the  end  of  the  reaction  by  being  decolorized  when 
used  as  an  oxidizer.  It  is  thus  useful  in  estimating 
ferrous  salts,  which  it  oxidizes  to  ferric  salts  when 
in  acid  solution.  The  end  of  the  reaction  is  known 
to  be  at  hand  when  decolorization  ceases  to  be  com- 
plete, the  end  point  being  reached  when  the  liquid 
acquires  a  faint,  permanent  pink  tint. 

Potassium  permanganate  is  also  used  in  the  esti- 
mations of  sulphur,  hypophosphites,  thiosulphates, 
oxalates,  and  hydrogen  peroxide. 

REFLECTING  GALVANOMETER 

The  reflecting  galvanometer  has  but  very  recently 
been  employed  by  Prof.  Kiister  as  a  physico-chemical 
substitute  for  the  indicators  commonly  employed  in 
titrations.  As  is  well  known,  many  mixtures  offer 
very  serious  obstacles  to  the  analyst,  at  times  so 


148  JNDICA  TORS 

great  as  to  render  the  ordinary  analytical  methods 
useless,  and  permit  accurate  results  to  be  obtained 
only  by  circuitous  and  tedious  means.  In  these  cases 
the  author  has  found  a  reflecting  galvanometer  to  be 
of  great  use.  For  instance,  if  potassium  permanganate 
is  gradually  added  to  a  solution  containing  free  iodine, 
potassium  iodide,  potassium  bromide,  and  potassium 
chloride,  and  which  has  been  acidulated  with  sulphuric 
acid,  it  will  be  found  that  the  iodine  of  the  iodide  will 
be  liberated  first  by  the  oxidation,  and  only  after 
this  will  further  oxidation  result  in  the  liberation  of 
free  bromine  and  in  the  formation  of  iodic  acid. 

Since  these  different  oxidation  processes  are  accom- 
panied by  decidedly  varying  electrical  potentials,  a 
reflecting  galvanometer,  interposed  in  the  circuit  by 
means  of  suitable  electrodes,  will  exhibit  a  very 
decided  and  sudden  deviation  as  soon  as  the  oxidation 
of  the  iodide  is  at  an  end  and  that  of  the  bromide 
begins.  The  deviation  here  takes  the  place  of  the 
color-change  afforded  by  the  indicators  ordinarily  used 
in  titration.  The  results  obtained  in  titrations  by 
means  of  the  reflecting  galvanometer  are  stated  to  be 
in  no  wise  inferior  to  those  obtained  by  the  employ- 
ment of  good  indicators.  The  application  of  the 
galvanometer  is  certainly  a  novel  one,  and  deserves  to 
be  carefully  tested. 


RESAZURIN  149 

RESAZURIN 

C,  8H10NaO6?  or  :  C,,H7NO4?  or  :  C,aH9NO4  ? 

ALKALIES  =  Blue  ACIDS  =  Red 

Synonyms:  Azoresorcin  ;  Diazoresorcin  ;  Resa- 
zoin  ;  Weselsky's  Indicator;  Crismer's  Indicator. 

Preparation  :  Resazurin  is  obtained  by  dissolving 
4  Gm.  of  resorcin  in  300  Cc.  of  anhydrous  ether, 
and  then  adding  40  or  45  drops  of  fuming  nitric 
acid  (sp.  gr.  1.25,  and  prepared  by  the  action  of 
nitric  acid  on  starch).  After  standing  in  a  cold 
(—  5°  to  —  8°C.)  place  for  2  days,  the  blackish  or 
brownish-red  crystals  are  separated  from  the  red 
liquid  holding  in  solution  resorufin  and  other  nitro- 
resorcins,  by  decanting.  The  crystals  are  then 
washed  with  ether,  and  finally  with  water,  until  the 
washings  have  a  pure  blue  color  free  from  any  violet 
tint  (which  would  indicate  the  presence  of  some 
resorufin).  Resazurin  is  also  formed  by  the  action 
of  manganese  dioxide  and  sulphuric  acid  on  an 
alcoholic  solution  of  resorcin  and  nitrosoresorcin. 

Properties  :  Resazurin  occurs  as  reddish-brown 
crystals,  slightly  soluble  in  water,  more  so  in 
alcohol,  and  quite  soluble  in  acetic  ether.  It  is  a 
monobasic  'acid,  and  is  easily  decomposed  by 
alkalies.  Considerable  confusion  appears  to  exist 
regarding  its  compositionc  According  to  Weselsky 


I  50  INDICA  TORS 

and  Benedikt  it  appears  to  have  the  composition 
CI8H10N3O6,  and  to  be  formed  as  follows  : 
3G.H  A  +  2NOa  =  C18H10NaOe  4-  4H3O.  Accord- 
ing  to  Brunner  and  Kramer,  it  is  formed  thus  : 
2CBH4(OH),  +  4NaO  =  C18H9N04  +  2 HaO.  The  for- 
mulas  CltH,NO4  and  Cl8HiaN,Oe  have  also  been 
assigned  it. 

Application:  Resazurin  is  a  comparatively  new  indi- 
cator, and  was  proposed  for  use  by  Crismer.  A  so- 
lution of  O.2  Gm.  of  resazurin,  40  Cc.  of  decinormal 
ammonia,  and  sufficient  water  to  make  1000  Cc. 
affords  an  extremely  sensitive  means  for  titrating 
alkalies.  This  solution  has  a  deep-blue  color  by 
reflected  light,  but  a  red  by  transmitted  light,  and  is 
quite  stable  ;  2  or  3  drops  suffice  for  200  Cc.  of 
liquid  to  be  titrated.  The  blue  color  of  the  solution 
is  changed  to  red  by  acids,  and  restored  by  alkalies 
and  carbonates  of  alkalies. 

Resazurin  is  especially  serviceable  for  titrating 
decinormal  sodium-borate  solution,  for  which  neither 
litmus  nor  phenolphtalein  will  answer.  On  the  other 
hand  it  is  unsuitable  for  nitric  acid  or  monobasic 
organic  acids,  the  indications  being  too  uncertain.  It 
is  also  sensitive  to  carbonic  acid,  but  much  less  so 
than  litmus  or  phenolphtalein. 

Resazurin  is  so  delicate  a  reagent  for  alkalies, 
that  water  boiled  in  a  Florence  flask  is  colored  blue 
by  it,  due  to  the  alkalinity  produced  by  some  of  the 
glass  entering  into  solution. 


RESOR  CINBENZEIN  1 5 1 

A  test-paper  is  also  prepared,  and  is  noted  under 
Test-papers. 

RESORCINBENZEIN 

C9H6.C.C8H8(OH)3.C8HS.O.OH 
ALKALIES^  Yellowish-brown      AciDS= Yellowish-red 

Preparation  :  Resorcinbenzein  is  obtained  by  warm- 
ing a  mixture  of  2  molecular  weights  of  resorcin 
with  I  molecular  weight  of  benzotrichloride,  and 
then  raising  the  temperature  to  i8o°-i9O°  C., 
when  vapors  of  hydrochloric  acid  are  evolved.  The 
reaction  that  takes  place  may  be  expressed  as  fol- 
lows : 


benzotrichloride  resorcinbenzein 


A  deep,  reddish-brown,  fused  mass,  having  a 
metallic  reflection,  is  thus  obtained.  The  mass  dis- 
solved in  dilute  soda  lye,  and  precipitated  by  add- 
ing acetic  acid,  in  the  form  of  yellow  crystals, 
which  are  finally  recrystallized  from  a  mixture  of 
alcohol  and  glacial  acetic  acid. 

Properties  :  Resorcinbenzein  crystallizes  from  a  mix- 
ture of  glacial  acetic  acid  and  alcohol  in  the  form  of 
prisms  which  are  violet-red  when  viewed  by  reflected 
light,  but  yellow  by  transmitted  light. 

The   precipitated   product   is  soluble  in  alcohol, 


IS2  .INDICATORS 

but  the  crystals  are  difficultly  so,  and  more  readily 
soluble  on  adding  hydrochloric  or  acetic  acid. 

Resorcinbenzein  yields  yellowish-red  solutions 
having,  when  dilute,  a  green  fluorescence.  Alkalies 
change  the  color  to  a  yellowish-brown. 

Application  :  The  indicator  is  rarely  if  ever  used. 
It  appears  to  possess  no  advantages  over  other 
indicators,  but  may  be  used  like  the  other  benzotri- 
chloride  derivatives  of  phenols. 

ROSE   COLORING-MATTER 

ALKALIES  =  r  DeeP  red  with       ACIDS  =  Light-red 
Green  Fluorescence 

Preparation  :  The  coloring-matter  of  rose  leaves, 
Rosa  Gallica,  was  obtained  by  Harold  Senier  by 
digesting  the  leaves  with  ether,  whereby  the  fat 
and  quercetin  were  removed,  and  after  filtering, 
extracting  the  coloring-matter  with  alcohol.  By 
this  means  a  colorless  solution  is  obtained,  which 
acquires  a  color  with  age.  Water  may  also  be  used 
to  extract  the  coloring-matter,  and  in  this  case  the 
solution  is  colored.  From  the  alcohol,  the  coloring- 
matter  was  precipitated  by  lead  acetate  as  a  green 
lead  compound,  which  was  then  washed,  dried,  and 
finally  decomposed,  either  by  a  current  of  hydrogen 
sulphide  while  suspended  in  water,  or  by  the  addi- 
tion of  sulphuric  acid.  By  this  means  a  bright-red 


ROSOLIC  ACID,    COMMERCIAL  153 

solution  of  the  coloring-matter  was  obtained,  which 
yielded  the  matter  on  evaporation. 

Properties  :  A  solution  of  the  coloring-matter  of  rose 
leaves  is  brightened  by  acids ;  alkalies  change  the 
color  to  a  deep  red  with  green  fluorescence.  Car- 
bonates of  the  alkalies  act  like  the  alkalies,  but  the 
change  is  accompanied  by  effervescence,  carbon 
dioxide  being  evolved.  Hydrogen  sulphide  destroys 
the  color,  changing  it  brown;  stannic  chloride 
changes  it  a  magenta.  Mercuric  nitrate  and  chloride 
yield  with  the  coloring-matter  a  white  and  pink 
precipitate  respectively.  With  barium  and  calcium 
hydrates,  yellowish-green  precipitates  are  afforded, 
which,  on  drying,  become  brown.  The  coloring- 
matter  has  the  properties  of  a  weak  acid,  and  its 
solution  exhibits  an  acid  reaction. 

Application  :  The  coloring-matter  of  rose  leaves  is 
rarely  used,  as  it  possesses  no  advantages  over  the 
more  commonly  used  indicators. 

ROSOLIC  ACID,  COMMERCIAL 

(C,H4OH)2.C6H4CO 

ALKALIES  =  Rose-red  ACIDS  =  Yellow 

Synonyms:  Para-rosolic  Acid;  Aurin ;  Corallin ; 
Aurin  Red. 

^reparation :  Commercial  rosolic  acid  is  a  mixture 
of  aurin,  C19H14O,,  oxidized  aurin,  C,9H16O6,  methyl- 
aurin,  C?0HJ6O,,  and  pseudorosolic  acid,  C,0H10O4, 


I  54  IN DIC A  TORS 

but  chiefly  the  last.  It  is  obtained  by  heating  a 
mixture  of  6  parts  of  phenol,  3  parts  of  sulphuric 
acid,  and  4  parts  of  anhydrous  oxalic  acid  (the  last 
being  gradually  added)  to  a  temperature  of  from 
1 30°  to  150°  C.,  for  5  to  6  hours,  or  until  the  libera- 
tion of  gas  ceases.  The  reaction  occurs  between 
the  phenol  and  oxalic  acid,  and  is  shown  to  take 
place  as  follows : 

3C6H80  +  C,H304  =  CI9H140,  +  CH,02  +  2HaO 

phenol  oxalic  acid  aurin  formic  acid 

The  product  of  the  reaction  is  boiled  with  water  in 
order  to  purify  it,  and  is  then  dried. 

Rosolic  acid  is  also  obtained  by  heating  phenol 
with  formic  acid  and  tin  chloride;  on  boiling  diazo- 
pararosaniline  with  water;  by  heating  together 
dioxybenzophenon  chloride  and  phenol ;  and  also 
by  the  action  of  salicylaldehyde  on  phenol  in  the 
presence  of  sulphuric  acid. 

Properties  :  Commercial  para-rosolic  acid  occurs  as 
yellowish-brown  resinous  lumps  having  a  greenish 
fracture,  and  affording  a  yellow  powder.  It  is  in- 
soluble in  water,  but  is  soluble  in  alcohol  to  the  ex- 
tent of  50  per  cent.,  the  solution  having  a  yellow 
color.  It  is  also  soluble  in  glacial  acetic  acid,  and 
may  be  obtained  by  crystallization  from  alcohol  in 
the  form  of  dark-red,  rhombic  crystals,  or  red 
needles  with  greenish  luster,  which  decompose  when 
heated  above  220°  C.,  but  do  not  melt. 


KOSOLIC  ACID,    COMMERCIAL  1 55 

With  sulphuric  acid  para-rosolic  acid  yields  a 
yellow  solution ;  with  alkalies,  a  handsome  cherry 
red.  With  the  bisulphites  of  the  alkalies  it  yields 
colorless,  readily  soluble  compounds,  which  are 
decomposed  by  acids.  With  hydrochloric  acid  it 
gives  very  unstable  compounds.  By  reducing- 
agents  para-rosolic  acid  is  converted  into  leuko- 
aurin  (C19H16O,,  trioxytriphenylmethane).  At  a 
temperature  of  120°  C.  it  is  converted  into  para- 
rosaniline. 

Tests  :  0.5  Cc.  of  a  \<f>  solution  in  60$  alcohol,  added 
to  100  Cc.  of  the  solution  to  be  titrated,  requires 
0.7  Cc.  of  centinormal  hydrochloric  acid,  0.8 
Cc.  of  centinormal  ammonia,  and  4.1  Cc.  of 
centinormal  potassium  hydrate  to  effect  changes  of 
color. 

Application  :  Solution  of  para-rosolic  acid  for  titri- 
metric  use  is  made  by  dissolving  I  Gm.  of  the 
substance  in  100  parts  of  60$  alcohol ;  of  this  solution 
about  0.5  Cc.  are  used  for  100  Cc.  of  the  solution 
to  be  titrated. 

With  caustic  alkalies  and  their  carbonates,  and 
also  with  baryta  solution,  the  indicator  affords  a 
fine,  rose-red  color,  changed  by  acids,  even  carbonic 
acid,  to  a  yellow.  Para-rosolic  acid  yields  very 
sharp  end-reactions  in  the  presence  of  notable 
quantities  of  the  sulphates,  nitrates,  and  chlorides  of 
the  alkalies  and  of  barium,  calcium,  and  magnesium 
(at  least  the  soluble  salts).  When  ammonium  salts 


IS6  INDICATORS 

are  present,  however,  the  indicator  is  useless.  It  is 
serviceable  for  use  by  artificial  light.  The  total 
alkalinity  of  a  solution  may  be  titrated  with  the 
indicator,  but  the  solution  to  be  titrated  must  be 
boiled  during  the  operation  to  expel  carbonic-acid 
gas,  which  affects  the  indicator. 

For  ammonia,  para-rosolic  acid  is  not  as  good  as 
litmus.  Sulphides  of  the  alkalies  yield  a  red  color 
with  the  indicator,  but  on  adding  an  acid,  the  lib- 
erated hydrogen  sulphide  destroys  the  color ;  if  the 
solution  be  boiled  to  expel  the  gas,  the  color  is 
restored,  hence  titrations  of  sulphides  must  be  ef- 
fected in  hot  liquids. 

With  sulphides,  para-rosolic  acid  yields  a  sharp 
change.  In  cold  solutions,  normal  calcium  sulphide 
is  practically  neutral,  but  is  distinctly  alkaline  in 
boiling  solutions.  With  arsenates  the  result  is  poor; 
with  arsenites,  good. 

The  indicator  is  useless  for  acetic  acid,  because 
the  acetates  of  potassium  or  sodium  formed  act  to- 
ward the  para-rosolic  acid  like  alkalies. 

Care  must  be  taken  not  to  mistake  for  the  com- 
mercial rosolic  acid  the  true  rosolic  acid,  trioxy' 
diphenyl-carbinol  anhydride,  also  known  as  rosaurin, 
and  which  is  obtained  by  the  action  of  nitrous  acid 
on  rosaniline. 


SALICYLIC  ACID  157 

SALICYLIC  ACID 

C,H4(OH)CO9H 

ALKALIES  =  Yellow  ACIDS  =  Vi?1^,  then 

Colorless 

Synonym  :  Weiske's  Indicator. 

Preparation  :  The  salicylic  acid  most  commonly  found 
on  the  market  is  that  obtained  synthetically,  by  the 
action  of  carbon  dioxide  on  phenol,  according  to 
various  processes.  The  oldest,  and  probably  simplest, 
of  these  is  that  of  Kolbe.  This  process  consists  in 
saturating  phenol  with  caustic  soda,  so  that  sodium 
phenate,  C6H6ONa,  is  formed,  the  solution  being 
then  dried  on  a  water-bath  and  powdered.  This  is 
now  introduced  into  an  iron  retort,  and  heated  to 
100°  C.  on  an  oil-bath,  dry  carbon  dioxide  being 
then  conducted  into  it,  while  the  temperature  is 
gradually  raised.  When  the  temperature  has  reached 
170°  to  1 80°  C.  the  phenol  begins  to  distill  over,  half 
the  quantity  present  being  obtainable  in  this  man- 
ner. The  temperature  is  however  raised  still  more, 
carbon  dioxide  being  continuously  conducted  into 
the  retort,  and  when  220°  C.  has  been  reached,  and 
no  more  phenol  is  distilled  over,  the  operation  is  at 
an  end.  The  residue  in  the  retort,  which  consists  of 
disodium  salicylate,  is  dissolved  in  water,  and  hydro- 
chloric acid  added  to  precipitate  the  salicylic  acid. 
This  is  then  purified  either  by  neutralizing  with 
calcium  carbonate,  and  decomposing  the  calcium 


1 58  INDICATORS 

salicylate  with  hydrochloric  acid  ;  or  by  distilling  the 
salicylic  acid  with  superheated  steam ;  or  by  dialys- 
ing  the  hydro-alcoholic  solution  of  the  salicylic  acid. 
Two  reactions  occur  in  the  above  process.  The 
first  is  the  formation  of  sodium  phenylcarbonate, 
thus: 

C6H6ONa  +  CO,  =  CO,.C6H6.Na 

sodium  phenate  sodium  phenylcarbonate 

This    latter,   on    heating,   then  becomes   converted 
into  sodium  salicylate,  as  follows: 

CO,.CeH..Na  =  C6H4.OH.CO3Na 

sodium  salicylate 

Properties  :  Salicylic  acid  occurs  as  colorless,  odor- 
less, acicular  crystals  forming  a  bulky  mass  having 
a  rather  sweetish-sour,  astringent  taste.  It  is  soluble 
in  about  500  parts  of  water  at  15°  C.,  and  in  about 
15  parts  of  boiling  water;  in  2.5  parts  of  alcohol,  in 
2  of  ether,  in  80  of  cold  chloroform,  in  3.5  amylic 
alcohol,  in  60  of  glycerin,  in  80  benzene,  and  in 
about  65  parts  of  oils.  Various  salts,  such  as  sodium 
phosphate,  borax,  ammonium  acetate,  ammonium 
citrate,  etc.,  greatly  increase  its  solubility  in  water. 
Its  specific  gravity  is  1.443  to  1.457,  and  its  melting- 
point  lies  between  156°  and  157°  C.  Salicylic  acid 
may  be  sublimed  when  carefully  heated.  If  rapidly 
heated,  however,  ij:  decomposes  into  phenol  and 
carbon  dioxide. 

Salicylic  acid  and  its  salts  yield   with  ferric   salts 


SANTALn?  159 

a  violet  color,  which  is  destroyed  by  strong  acids. 
With  silver  nitrate  it  yields  a  white  precipitate. 
On  heating  with  methyl  alcohol  and  concentrated 
sulphuric  acid,  the  characteristic  odor  of  wintergreen 
oil  (methyl  salicylate)  is  observed.  Bromine  water 
affords  even  in  dilute  solutions  a  crystalline  precip- 
itate of  bromated  salicylic  acid. 

Application  :  Salicylic  acid  was  recommended  as  an 
indicator  by  Weiske.  The  solution  for  use  is  pre- 
pared by  adding  a  drop  of  ferric-chloride  solution  to 
a  hydro-alcoholic  solution  of  salicylic  acid,  and  then 
cautiously  adding  caustic  alkali  until  exact  neu- 
trality, evidenced  when  a  brownish-red  color  is 
formed.  A  small  quantity  of  the  solution  so  ob- 
tained is  added  to  the  acid  to  be  titrated,  when  a 
violet  color  first  develops,  which  is  decolorized  by 
strong  acids,  but  not  by  acetic  acid.  On  adding  an 
alkali,  however,  the  color  passes  again  through 
violet,  and  suddenly  into  yellow,  ferric  hydrate 
being  precipitated. 

SANTALIN 

CJ.HMO.  (?)     or:     C17HJ60«(?) 

ALKALIES  =  Violet  ACIDS  =  Red 

Synonym  :     Santalic  Acid. 

Source  :  Santalin  is  a  coloring-matter  obtained  from 
red  sandal- wood, Pterocarpussantalinus\^.,  one  of  the 


l6o  INDICATORS 

Leguminosae  indigenous  in  India,  and  also  found  in 
the  mountains  of  Coromandel  and  Ceylon.  It  was 
first  isolated  and  named  by  Pelletier,  who  observed 
it  to  possess  the  properties  of  an  acid.  This  obser- 
vation was  later  on  confirmed  by  Leo  Meier,  in 
1849,  who  also  named  the  preparation  "santalic 
acid." 

Preparation  :  Meier's  process  for  obtaining  santalin 
is  to  first  exhaust  with  water  the  residue  obtained  by 
evaporating  the  alcoholic  or  ethereal  extract  of  the 
wood,  then  to  dissolve  it  in  alcohol,  and  precipitate 
it  with  an  alcoholic  lead-acetate  solution.  The  pre- 
cipitate of  lead  sahtalate,  after  treatment  with 
boiling  alcohol,  is  heated  with  a  little  alcohol  and 
diluted  sulphuric  acid,  and  the  blood-red  solution 
obtained  after  filtering  evaporated. 

The  santalin  so  prepared  may  be  obtained  perfectly 
pure,  according  to  Weyermann  and  Haffley,  by  pre- 
cipitating with  water  its  alcoholic  solution  acidu- 
lated with  a  little  hydrochloric  acid,  washing  the 
precipitate  with  water,  dissolving  in  alcohol,  and 
then  evaporating  to  dryness. 

Dussance  recommends  precipitating  the  alcoholic 
extract  of  the  wood  with  an  excess  of  lead  oxyhy- 
drate,  washing  the  precipitate  with  alcohol,  and 
dissolving  it  in  acetic  acid.  The  solution  is  then 
precipitated  by  adding  a  large  volume  of  water. 
The  santalin  so  obtained  is  said  to  be  impure,  how- 
ever. 


SANTA  LIN  l6l 

Properties  :  Santalin  occurs  as  a  crystalline,  inodor- 
ous, tasteless  powder  of  a  handsome  red  color;  or 
in  the  form  of  red  prisms.  It  is  insoluble  in  water, 
but  is  soluble  in  alcohol,  ether,  acetic  acid,  and 
turpentine  oil.  It  is  also  soluble  in  concentrated 
sulphuric  acid  with  a  deep-red  color,  and  in  volatile 
oils  of  cinnamon,  lavender,  rosemary,  cloves,  berga- 
mot,  and  bitter  oil  of  almonds,  but  is  insoluble  in  • 
most  fixed  oils. 

It  is  present  to  the  extent  of  about  1 6$  in  sandal- 
wood,  and  its  composition  is,  according  to  Weyer- 
mann  and  Haffley,  C15H14OB;  it  is  C17H16O,  accord- 
ing to  Franchimont,  who,  however,  obtained  the 
santalin  in  an  amorphous  form  only. 

Santalin  possesses  the  properties  of  a  weak  acid, 
and  its  alcoholic  solution  has  an  acid  reaction. 
With  lime,  baryta,  and  salts  of  the  heavy  metals  it 
yields  insoluble  lakes.  Muspratt  appears  to  have 
shown  that  sandal  wood  contains  two  dyes,  one  of 
which  is  formed  from  the  other  by  oxidation.  Old, 
deeply  colored  woods  are  believed  to  contain  the 
oxidation  product,  whereas  fresh  and  unchanged 
woods  contain  the  unoxidized  dye.  In  aqueous 
solutions  of  the  alkalies,  santalin  dissolves  with  a 
violet  color,  which  is  changed  to  red  by  acids. 

Application  :  Santalin  is  rarely,  if  ever,  used  now 
as  an  indicator,  as  it  possesses  no  marked  advan- 
tages. 


1 62  INDICATORS 

SODIUM    SALICYLATE 

FERRIC  SALTS=Violet        FERROUS  SALTS  =  Colorless 

Preparation  :  Sodium  salicylate  may  be  made  extem- 
poraneously by  mixing  60  parts  of  pure  sodium  bicar- 
bonate (or  37.8  parts  of  anhydrous  carbonate)  and 
100  parts  of  salicylic  acid,  with  100  parts  of  diluted 
alcohol,  gradually,  and  then  drying,  after  the  reac- 
tion is  completed,  on  a  water-bath  at  a  moderate  heat. 
Commercially  the  salt  is  obtained  as  in  the  pro- 
cess described  in  the  preparation  of  salicylic  acid. 

Properties:  Pure  sodium  salicylate  forms  small, 
white  crystalline  plates,  or  a  crystalline  powder, 
permanent  in  the  air,  odorless,  having  a  sweetish 
taste,  and  a  feebly  acid  reaction.  It  is  soluble  in 
1.5  parts  of  water,  and  in  6  parts  of  alcohol  ;  it  is 
very  soluble  in  boiling  water  and  in  boiling  alcohol. 
The  salicylate  should  be  kept  in  dark  or  amber 
bottles. 

Application  :  Sodium  salicylate  has  been  used  as  an 
indicator  in  titrating  ferric  salts  with  sodium  thio- 
sulphate.  The  violet  color  of  ferric  salts  is  dis- 
charged at  the  end  of  the  reaction. 

STARCH 

C«H100. 

IODINE  =  Blue 

Source  :  Under  the  name  of  "  Starch  "  is  recognized 
the  fecula  obtained  from  various  graminaceous 


S '7 'ARCH  163 

plants,  solanaceous  tubers,  etc.,  the  principal  varie- 
ties being  obtained  from  wheat,  potatoes,  arrowroot, 
rye,  rice,  maize,  sweet  potatoes,  oats,  etc.  It  is  also 
found  in  large  quantities  in  peas,  beans,  chestnuts, 
etc. 

Preparation :  Starch  is  obtained  by  reducing  the 
seeds,  tubers,  etc.,  containing  it,  to  a  state  of  mi- 
nute division,  agitating  with  cold  water,  and  collect- 
ing and  drying  the  fecula  after  it  has  subsided. 

Properties:  Starch  is  too  well  known  to  require  any 
lengthy  description.  It  will  suffice  to  say  that  it 
occurs  generally  as  a  fine  white  powder,  or  in  the 
form  of  irregular,  sometimes  columnar,  masses  read- 
ily reducible  to  powder.  The  starch  granules  are 
insoluble  in  cold  water,  but  with  boiling  water  the 
enveloping  coat  bursts,  and  the  contents  swell  up 
and  dissolve,  yielding  a  thick  paste,  which,  on 
drying,  forms  a  horny,  translucent  mass.  Its 
formula  is  believed  to  be  CeH10O5,  or  a  multiple  of 
this. 

Application  :  Starch  solution  is  exceedingly  useful  as 
an  indicator  in  the  titration  of  iodine,  by  means  of 
sodium  thiosulphate.  With  the  minutest  traces  of 
iodine  it  affords  a  characteristic,  intensely  blue  color, 
visible  even  in  solutions  containing  the  iodine 
yielded  by  one  part'of  potassium  iodide  in  600,000 
parts  of  water  at  o°  C. 

It  is  also  used  in  the  titration  of  arsenous  acid, 


164  IND  1C  A  TORS 

sulphites  and  sulphurous  acid,  thiosulphates,  chlorine, 
ferric  salts,  and  hydrogen  dioxide. 

The  solution  for  use  is  made  by  triturating  I  part 
of  starch  with  a  little  cold  water,  and  then  adding 
200  parts  of  boiling  water,  under  constant  stirring. 
The  solution  is  then  set  aside  to  cool,  when  it  is  fil- 
tered or  allowed  to  settle.  It  is  then  ready  for 
use. 

Starch  solution  is  prone  to  spoil,  hence  preserva- 
tives are  frequently  added,  the  substances  most 
generally  employed  being  sodium  chloride,  zinc 
chloride,  calcium  chloride,  or  salicylic  acid.  Zinc 
chloride  has  the  best  preservative  powes;,  but  starch 
solution  preserved  by  means  of  it  cannot  be  used 
with  sulphides  or  when  hydrogen  sulphide  is  lib- 
erated, and  with  a  carbonate  is  prone  to  yield  a  dis- 
turbing precipitate;  sodium  chloride  is  least  valua- 
ble, but  interferes  least  in  the  application  of  the 
indicator,  hence  it  is  preferred ;  calcium  chloride, 
proposed  by  Fluckiger,  is  good,  but  also  yields  a 
precipitate  with  a  carbonate ;  salicylic  acid  is  also 
good,  but  cannot  be  used  in  the  presence  of  sodium 
carbonate,  because  it  then  itself  decolorizes  iodine 
solutions. 

A  spoiled  starch-solution  must  not  be  employed, 
because  it  no  longer  gives  a  blue,  but  a  brown,  color 
with  iodine. 


TETRABROMOPHENOLPHTALEIN  l6$ 

TETRABROMOPHENOLPHTALEIN 

C202.C8H4(C6HaBraOH)a 

ALKALIES  —  Violet  ACIDS  =  Colorless 

Preparation  :  Tetrabromophenolphtalein  is  prepared 
by  adding  a  mixture  of  10  parts  of  bromine 
and  10  parts  of  glacial  acetic  acid  to  a  boiling 
solution  of  5  parts  of  phenolphtalein  and  20  parts 
of  alcohol. 

Properties  :  Tetrabromophenolphtalein  crystallizes 
from  ether  in  the  form  of  colorless  needles  that 
melt  between  220°  and  230°  C.  with  decomposition. 
They  are  difficultly  soluble  in  alcohol  and  in  glacial 
acetic  acid,  but  readily  soluble  in  ether.  They 
are  dissolved  by  alkalies  with  a  violet  color,  which, 
however,  immediately  disappears  on  adding  an 
excess  of  alkali,  from  the  formation  of  an  acid 
having  the  composition  C,0H,.,Br4OB .  On  heating 
with  warm  sulphuric  acid,  dibromoxyanthraquinone 
is  formed.  Solutions  made  violet  by  alkalies  are 
rendered  colorless  on  addition  of  acids. 

Application :  Tetrabromophenolphtalein  has  been 
proposed  for  use  in  cases  similar  to  those  in  which 
phenolphtalein  is  used.  It  appears  to  be  in  no 
wise  superior  to  the  latter,  however. 


1 66  INDICA  TORS 

THYMOLPHTALEIN 
C,O,.C.H4.(C.H,.CH,.C,H,.OH), 

ALKALIES  =  Blue  ACIDS  =  Colorless 

Preparation:  Thymolphtalein  is  prepared,  according 
to  M.  C.  Traut,  as  follows:  Equal  parts  of  thymol, 
phtalic  acid,  and  zinc  chloride  are  treated  in  a  flask 
at  a  temperature  not  exceeding  150°  C.  until  the 
melted  mass,  which,  under  proper  conditions,  has  a 
handsome  red  color,  flows  quietly.  The  mass  is 
washed  first  with  very  dilute  hydrochloric  acid, 
then  with  water,  and  finally  with  benzin  to  remove 
unchanged  thymol.  The  residual  thymolphtalein 
is  purified  by  repeated  treatment  with  ether,  and  re- 
crystallization  from  a  mixture  of  ether  and  alcohol. 

Properties  :  Thymolphtalein  forms  colorless,  prismatic 
needles,  easily  soluble  in  alcohol,  less  readily  so  in 
benzene,  ether,  or  chloroform,  and  only  very  slightly 
so  in  water.  It  melts  between  252°  and  254°  C. 
Its  alcoholic  or  aqueous  solution  is  colorless,  but 
develops  an  intense,  blue  color  on  the  addition  of 
traces  of  alkali,  the  solutions  appearing  reddish  by 
transmitted  daylight,  but  decidedly  red  by  trans- 
mitted artificial  light.  The  blue  color  is  discharged 
on  the  addition  of  an  acid. 

Application  :  Thymolphtalein,  it  is  claimed,  is  equally 
as  serviceable  as  phenolphtalein,  and  may  be  used 
like  the  latter. 


TOLUYLENE  RED  1 67 

TOLUYLENE    RED 

(CH3)a.N.C8H4.NH.(NHa)C7H6 

ALKALIES  =  Yellow  ACIDS  =  Red 

Synonym:     Neutral  Red. 

Preparation  :  Toluylene  red  was  discovered  in  1879 
by  O.  N.  Witt.  It  is  prepared  by  simply  boil- 
ing an  aqueous  solution  of  toluylene  blue.  It  is, 
also  obtained  by  the  oxidation  of  a  mixture  of  equal 
molecular  weights  of  dimethylparaphenylenediamine 
and  metatoluylenediamine  at  the  boiling  point. 

Properties:  Toluylene  red  forms  orange-red  needles 
containing  4  molecules  of  water  of  crystallization, 
and  having  the  composition 

(CH,).NC.H..NH.(NH,)C,H.. 

At  a  temperature  of  150°  C.  it  is  converted  into  the 
blood-red  anhydrous  modification.  It  also  occurs 
as  a  greenish-black  powder,  easily  soluble  in  water 
with  a  crimson  color,  and  in  alcohol  with  a  magen- 
ta-red, having  a  faint  brownish-red  fluorescence. 
With  alkalies  it  yields  an  intense,  yellow  color, 
restored  to  red  by  acids. 

Application  :  Toluylene  red  is  rarely  used ;  it  pos- 
sesses no  advantages  whatever  over  other  indicators. 


1 68  INDICA  TORS 

TROP^OLIN   OO 

C.H4.SO,Na.Na.C,H4NH.C8H§ 
ALKALIES  =  Yellow       ACIDS  =  Yellowish-red  to  Red 

Synonyms:  Orange  GS.  ;  Orange  N.  ;  Orange  iv; 
New  Yellow;  Fast  Yellow;  Acid  Yellow  D.  ; 
Diphenylamine  Orange;  Orange  M.  ;  Diphenyla- 
mine  Yellow;  Von  Muller's  Indicator. 

Preparation  :  Tropaeolin  OO  is  prepared  by  heating 
5  parts  of  fuming  sulphuric  acid  (20$  anhydride) 
and  I  part  of  phenylamido-azobenzene  for  four 
hours  at  a  temperature  of  60°  to  70°  C.,  cooling, 
and  pouring  the  mass  into  50  parts  of  water.  The 
precipitate  is  then  collected,  washed,  and  converted 
into  a  sodium  salt,  which  is  the  commercial  form  of 
the  article. 

Properties  :  The  base,  phenylamido-azobenzene- 
sulphonic  acid,  forms  graphite-like  needles,  difficultly 
soluble  in  water  and  yielding  a  reddish-violet  solu- 
tion. 

The  sodium  salt  occurs  in  the  form  of  orange- 
yellow  scales  or  powder,  soluble  in  water  and 
yielding  an  orange-yellow  solution.  Its  composition 
is  NaSOs.CflH4.Na.C6H4.  =  NH.C6H6.  When  hydro- 
chloric acid  is  added  to  the  aqueous  solution,  a 
violet  precipitate  is  formed.  With  concentrated 
sulphuric  acid  it  affords  a  violet-colored  solution. 


OO  169 

Application  :  Tropaeolin  OO  was  recommended  by 
von  Miiller  as  an  indicator.  For  use  a  solution  of 
o.  5  Gm.  of  tropaeolin  OO  in  a  liter  of  water,  or  a  cold 
saturated  alcoholic  solution,  is  prepared;  2  Cc.  of 
the  aqueous,  or  a  few  drops  of  the  alcoholic,  solution 
are  added  to  50  Cc.  of  the  liquid  to  be  tested.  The 
light-yellow  solution  is  colored  yellowish-red  by 
acids,  even  by  oxalic  and  other  organic  acids  ;  on 
adding  an  excess  of  acid  a  red  color  is  obtained. 
Alkalies  restore  the  yellow  color. 

The  indicator  is  not  affected  by  free  carbonic-acid 
gas,  bicarbonates,  or  by  acid  salts,  in  which  respect 
it  is  superior  to  litmus,  because  normal  sodium- 
carbonate  solution  may  be  used  instead  of  caustic- 
soda  solution  for  titrating. 

The  color  of  tropaeolin  OO  is  changed  to  red 
only  by  free  acids,  and  not  by  solutions  of  metallic 
salts.  Hence  small  quantities  of  added  acids  may 
be  readily  determined.  Hydrogen  sulphide  also 
does  not  affect  the  indicator. 

Tropaeolin  OO  must  be  employed  only  in  cold 
solutions. 

Tropaeolin  OO  is  a  good  indicator,  but  its  quality 
cannot  IDC  depended  on ;  hence,  readings  given  by 
it  may  be  unreliable.  It  behaves  very  much  like 
methyl  orange,  but  is  less  sensitive  to  acids.  It 
may  be  distinguished  from  methyl  orange,  accord- 
ing to  Engel,  by  means  of  gold  chloride,  as  this 
affords  a  violet,  then  green  color  with  tropaeolin 


I/O  INDICATORS 

OO,   whereas  with    methyl   orange   it  yields  a  red 
color. 

The  indicator  is  also  used  in  the  form  of  a'  test- 
paper  (see  under  Test-Papers). 

TROP^EOLIN   OOO   No.  I 

CeH^Na.doHeOH.SOaNa 

ALKALIES  =  Brown  ACIDS  =  Brownish-yellow 

Synonyms :  Orange  II ;  Betanaphtol  Orange  ;  Man- 
darin G.  Extra  ;  Chrysaurein  ;  Gold  Orange  ; 
Orange  Extra ;  Atlas  Orange  ;  Orange  A ;  Sulpho- 
azobenzene-beta-naphtol. 

Preparation :  Tropaeolin  OOO  No.  2  is  obtained  by 
the  action  of  para-diazobcnzene-sulphonic  acid  on 
beta-naphtol  in  alkaline  solution,  the  process  being 
quite  similar  to  that  whereby  tropaeolin  OOO  No.  2 
is  prepared.  The  product  is  converted  into  the 
sodium  salt,  which  is  the  commercial  form  of  the 
article. 

Properties:  The  base,  C.H4.HSO3.Na.C10H6.HO, 
occurs  as  orange-yellow  scales  insoluble  in  water  ; 
on  drying  they  lose  water  and  are  converted  into  a 
red  powder. 

The  sodium  salt  occurs  as  a  bright  orange  powder, 
soluble  in  water  and  yielding  an  orange-colored 
solution.  On  adding  hydrochloric  acid  to  the  solu- 
tion it  occasions  a  brownish-yellow  flocculent  pre- 


TROP&OLIN   OOO   No.   2  I/I 

cipitate.  Caustic  alkalies  change  the  color  to  a 
dark  brown.  With  concentrated  sulphuric  acid  it 
yields  a  dark-red  solution  which,  on  dilution  with 
water,  becomes  a  reddish-brown. 

Application:      Like  Tropaeolin  OOO  No.  2. 
TROPAEOLIN   OOO   No.  2 

C8H4.S03Na.N2.C10H6(OH) 

ALKALIES  =  Red  ACIDS  =  Yellow 

Synonyms:  Orange  I;  Sodium  <*-Naphtolazoben- 
zene  Sulphonate  ;  Alpha-Naphtol  Orange  ;  Orange 
B.  ;  Naphtol  Orange;  Alpha-Naphtol  Yellow;  Sul- 
phoazobenzene-alpha-naphtol;  Von  Muller's  Indi- 
cator. 

Preparation  :  Tropaeolin  OOO  No.  2  is  prepared  as 
follows:  25  parts  of  caustic  soda  are  dissolved  in 
450  parts  of  boiling  water,  100  parts  of  sulphanilic 
acid  added,  and  the  solution  cooled,  when  64  parts 
of  sulphuric  acid,  and  finally,  41  parts  of  sodium 
nitrite  dissolved  in  200  parts  of  water  added.  To 
the  solution  so  obtained,  a  solution  prepared  by 
boiling  80  parts  of  alpha-naphtol  and  30  parts 
of  caustic  soda  in  400  parts  of  water,  is  slowly 
added  with  constant  agitation.  The  precipitate 
is  then  collected,  dried,  and  converted  into  the 
sodium  salt,  which  is  the  commercial  form  of  the 
article. 


I72  INDICATORS 

Properties:  The  acid  base  forms  almost  black  scales 
having  a  greenish  shimmer,  and  the  composition 
C.H4(SO,H).Na.  =  C:oHe(HO).  The  sodium  salt 
occurs  as  reddish-brown  powder,  readily  soluble  in 
water  and  yielding  an  orange-red  solution,  the  color 
of  which  is  changed  to  red  or  brownish-red  by 
alkalies.  In  concentrated  sulphuric  acid  it  dissolves 
with  a  magenta  color.  Its  solutions  yield  with 
hydrochloric  acid  a  brownish-yellow  coloration  or 
flocculent  precipitate. 

Application  :  Tropaeolin  OOO  was  recommended  as 
an  indicator  by  W.  von  Miiller.  For  use  a  cold, 
saturated,  aqueous  solution  is  most  suitable.  A  few 
drops  of  the  solution  are  added  to  the  liquid  to  be 
titrated.  This  colors  it  a  scarcely  perceptible 
yellow,  which  is  sharply  and  suddenly  changed  to 
red  by  alkalies.  Ammoniacal  salts  do  not  affect  it, 
nor  does  carbonic-acid  gas  ;  it  is,  hence,  applicable  in 
the  presence  of  the  latter. 

ZINC-IODIDE  AND  STARCH 

Preparation:  Zinc-iodide  and  starch  solution  is  pre- 
pared by  heating  4  parts  of  starch,  20  parts  of  zinc 
chloride,  and  100  parts  of  water  over  a  free  flame 
for  an  hour  or  more,  until  a  clear  solution  is  ob- 
tained, the  evaporated  water  being  replaced  from 
time  to  time.  Sufficient  water  is  then  added  to 
make  the  whole  measure  1000  Cc.,  and  the  mixture 


ZINC-IODIDE  AND    STARCH  1 73 

is  then  set  aside  for  a  week  or  two,  when  the  solu- 
tion is  filtered,  and  2  parts  of  zinc-iodide  then 
added. 

Application :  The  solution  is  used  in  iodometric  de- 
terminations as  an  indicator.  It  is  colored  blue  by 
the  slightest  traces  of  free  iodine. 


PART  III 


TEST-PAPERS 

FOR  the  preparation  of  test-papers  only  the  finest 
quality  of  filtering-paper  should  be  used,  and  even 
then,  before  impregnation  with  the  indicator-sub- 
stance, it  should  be  treated  with  very  dilute  hydro- 
chloric acid,  then  with  very  dilute  ammonia,  then 
again  with  the  hydrochloric  acid,  and  finally 
thoroughly  washed,  to  remove  all  traces  of  im- 
purities, with  plenty  of  recently  distilled,  freshly 
boiled  water,  and  finally  dried  in  an  ammonia-free 
atmosphere. 

The  paper  so  treated  is  immersed  in  the  indicator- 
solution,  the  surplus  of  the  latter  is  removed  by 
passing  the  paper  over  glass  rods  held  horizontally, 
and  the  paper  then  hung  over  stretched  cords,  or 
suspended  by  two  corners  by  means  of  clips.  When 
the  dripping  has  ceased,  the  paper  should  be  re- 
versed, i.e.,  hung  by  the  two  corners  that  had  been 
lowermost.  If  this  is  not  done,  the  paper,  when  dry, 
will  have  received  a  surcharge  of  the  indicator-sub- 


TES  T-PA  PERS  1 7  5 

stance  at  its  lower  end,  because  of  a  greater  quan- 
tity of  the  solution  having  accumulated  there  dur- 
ing the  hanging.  It  is  well,  therefore,  to  reverse 
the  position  of  the  paper  several  times  during  the 
period  it  is  drying,  in  order  to  insure  uniformity  of 
color  and  sensitiveness. 

During  the  drying  care  must  also  be  taken  that  the 
paper  be  not  exposed  to  ammoniacal,  acid,  or  sul- 
phurous fumes,  because  many  test-papers  are  ex- 
ceedingly sensitive  to  them,  and  may  in  consequence 
.suffer  an  impairment  of  delicacy  after  exposure  to 
them. 

Where  the  substance  to  be  applied  is  in  the  form 
of  a  paste,  as  in  making  ultramarine-,  starch-,  etc., 
papers,  the  paste  is  best  applied  by  means  of  a 
broad,  flat,  camel's-hair  brush,  care  being  taken  to 
touch  every  part  of  the  paper  but  once. 

Test-papers  are  used  either  by  dipping  directly 
into  the  liquid  to  be  tested,  and  observing  the  color- 
changes,  if  any,  that  occur;  or  better,  by  applying 
a  drop  or  two  of  the  solution  taken  up  on  a  glass 
rod  to  the  paper.  For  titrimetry  proper,  test- 
papers  are  not  very  serviceable,  as  a  rule,  because 
very  many  trials  must  be  made  before  the  end  re- 
action can  be  determined  with  precision.  This  oc- 
casions a  great  loss  of  time,  besides  rendering  the 
final  result  slightly  inaccurate  on  account  of  the 
withdrawal  of  repeated  appreciable  quantities  of  the 
liquid  being  titrated. 


1/  TEST-PAPERS 

For  the  qualitative  detection  of  metals,  etc,, 
however,  the  test-papers  are  excellent,  and  are  very 
serviceable. 

All  test-papers  should  be  preserved  in  dark,  or 
amber-colored,  carefully  stoppered  bottles,  and  be 
as  little  exposed  to  light  and  air  as  possible,  as  these 
have  a  disturbing  effect  on  a  very  large  number  of 
the  dyes  of  which  the  indicators  for  the  most  part 
consist. 

ALKANIN   PAPER 

ALKALIES  =  Green  or  Blue  ACIDS  =  Red 

Synonym:  Anchusin  Paper;    Boettger's  Test-Paper. 

Preparation  :  Paper  is  impregnated  with  a  3-per- 
cent, alcoholic  solution  of  alkanin,  or  with  an 
ethereal  extract  of  alkanet-root  bark.  The  paper 
so  obtained  possesses  a  rose-red  color  when  dry, 
and  should  be  very  carefully  preserved  in  an  am- 
monia-free atmosphere. 

Application  :  Alkanin  paper  is  extremely  sensitive 
to  free  alkalies  and  alkaline  salts,  and  particularly 
to  ammonia,  even  the  slightest  traces  of  which  color 
the  paper  green.  It  is  sensitive  to  a  1:25000 
solution  of  potassium  hydrate,  and  to  a  1:80000 
solution  of  ammonia. 

Blue  Alkanin  Paper  may  be  obtained  by  immers- 
ing the   red   paper,  prepared  as  above,  in  a  i-per- 


BENZOPURPURIN  PAPER  1/7 

cent,  solution  of  sodium  carbonate,  and  drying. 
This  paper  is  sensitive  to  a  1:60000  solution  of 
sulphuric  acid,  and  to  a  1 :  80000  solution  of  hydro- 
chloric acid. 

AZOLITMIN   PAPER 

ALKALIES  =  Blue  ACIDS  =  Red 

Preparation  :  Azolitmin  paper  is  prepared  by  im- 
pregnating filter-paper  with  a  solution  obtained  by 
dissolving  I  part  of  azolitmin  and  0.5  part  of 
crystallized  sodium  carbonate  in  1000  parts  of 
water,  and  adding  to  the  solution  just  sufficient 
phosphoric  acid  to  cause  a  faint  redness.  The 
paper  when  dry  has  a  reddish-violet  color  which 
is  changed  to  a  red  by  acids  and  to  a  blue  by 
alkalies. 

Application :  Azolitmin  paper  is  very  sensitive,  and 
it  is  used  like  litmus.  Before  use,  its  sensitiveness 
should  be  invariably  tested.  It  is  sensitive  to  sul- 
phuric acid  i  :  40000;  and  to  hydrochloric  acid 
I  :  5°  ooo,  according  to  Dieterich. 

BENZOPURPURIN   PAPER 

ALKALIES  =  Brownish-red          ACIDS  =  Bluish-violet 

Preparation :  A  solution  of  Benzopurpurin  B.  is 
made  violet  with  a  small  quantity  of  acid,  and  white 


178  TEST-PAPERS 

filtering-paper  impregnated   with   the   solution   and 
dried. 

Application :  Benzopurpurin  paper  affords  a  very 
sensitive  means  of  detecting  ammonia,  the  slightest 
traces  of  which  change  the  bluish-violet  color  of  the 
paper  to  a  red  on  drying. 

BRAZILIN   PAPER 

ALKALIES  =  Blue  ACIDS  =  Yellow 

Synonyms:    Pernambuco  Paper;  Fernambuco  Paper. 

Preparation  :  Unsized,  white  paper  is  impregnated 
with  a  solution  of  brazilin,  and  'dried;  or,  the  paper 
may  be  immersed  in  a  12.5-per-cent.  infusion  o£ 
Brazil  wood,  to  which  ammonia  has  been  added 
until  a  bluish-red  color  is  had,  and  dried. 

Application :  Brazilin  paper  is  very  sensitive  to  acids, 
and  may  be  used  in  their  estimation.  The  paper 
should  be  very  carefully  preserved  in  the  dark,  and 
from  air  as  much  as  possible. 

Concentrated  or  gaseous  hydrofluoric  acid,  and 
also  phosphoric  and  oxalic  acids,  have  no  action  on 
the  paper  until  water  has  been  added  to  the  con- 
centrated acids. 

The  paper  is  sensitive  to  I  :  80  coo  of  ammonia, 
and  to  a  i  :  30  ooo  solution  of  potassium  hydrate. 


CARMINE  PAPER  1 79 

BRUCINE   PAPER 

NITRIC  ACID  =  Red  CHLORINE  =  Red 

Preparation  :  Filter-paper  is  impregnated  with  an 
aqueous,  concentrated  solution  of  brucine  sulphate, 
and  dried  in  a  warm  place. 

Application  :  Brucine  paper  is  applied  for  the  detec- 
tion of  chlorine  and  nitric  acid. 

BUCKTHORN    PAPER 

ALKALIES  =  Greenish-yellow  AciDS  —  Red 

Preparation  :  Paper  is  immersed  in  a  decoction  of 
buckthorn  berries  (Rhamnus  cathartica),  and  dried. 

Application:  Buckthorn  paper  is  used  similarly  as 
georgina  paper.  Acids  change  its  color  to  red ; 
alkalies  to  a  greenish-yellow. 

The  paper  is  sensitive  to  a  i  :  15  ooo  solution  of 
potassium  hydrate,  and  to  a  I  :  3$  ooo  solution  of 
ammonia. 

CARMINE    PAPER 

ALKALIES  =  Purplish-red          ACIDS  =  Yellowish-red 

Preparation  :  A  red  carmine  paper  is  prepared  by 
immersing  pure  filter-paper  in  an  ammoniacal  solu- 
tion of  carmine. 

Application  :  The  carmine  paper  is  at  times  used  in 
analytical  work,  although  infrequently.  It  is  used 
like  the  carmine  tincture. 


ISO  TESI^-PAPERS 

CITRO-MERCURIC-CHLORIDE    PAPERS 

ALBUMIN  —  Precipitate 
Synonym :  Geissler's  Test-Papers. 

Preparation  :  Geissler's  test-papers  are  prepared  by 
saturating  strips  of  paper  with  a  concentrated  citric- 
acid  solution  and  drying;  other  strips  of  paper  are 
impregnated  with  a  solution  containing  3  per  cent, 
of  mercuric  chloride  and  from  12  to  15  per  cent,  of 
potassium  iodide. 

Application  :  The  papers  are  employed  for  the  detec- 
tion of  albumin  in  urine,  and  as  follows:  A  strip  of 
the  acid  paper  is  first  dipped  into  the  urine  to  be 
tested,  and  stirred  ;  then  a  mercury-potassium-iodide 
paper  is  immersed.  If  albumin  is  present  a  precip- 
itate forms. 

CITRO-MOLYBDIC-ACID   PAPER 

MOISTURE  =  Decolorization 
Synonym :    Mann's  Paper. 

Preparation:  One  part  of  molybdic  acid  and  two 
parts  of  citric  acid  are  fused  together,  and  then  dis- 
solved in  water.  With  the  solution  filtering-paper 
is  impregnated,  and  dried  at  a  temperature  of  100°  C. 

Application:  The  paper  is  blue  when  dry,  and  is 
applied  for  the  detection  of  water  in  alcohol,  etc., 
as  exposure  to  moisture  discharges  the  blue  color. 


CITRO-SODIUM-TUNGSTAl'E   PAPER  l8l 

CITRO-POTASSIUM-FERROCYANIDE 
PAPERS 

ALBUMIN  =  Precipitate 

Synonym  :  Oliver's  Albumin  Papers. 

Preparation  :  Some  strips  of  filtering-paper  are  im- 
pregnated with  a  concentrated  solution  of  citric 
acid,  while  other  strips  are  impregnated  with  a 
concentrated  solution  of  potassium  ferrocyanide. 
The  strips  are  then  dried. 

Application :  The  papers  are  used  for  detecting  the 
presence  of  albumin  in  urine.  For  this  purpose,  a 
strip  of  the  citric-acid  paper  is  first  stirred  in  the 
suspected  urine,  and  then  a  strip  of  the  ferrocyanide 
paper.  Albumin,  if  present,  occasions  a  precipitate. 

CITRO-SODIUM-TUNGSTATE  PAPER 

ALBUMIN  =  Precipitate 

Synonym  :   Oliver's  Tungstate  Paper. 

Preparation:  Paper  is  immersed  in  a  strong  solution 
of  sodium  tungstate  and  citric  acid,  and  then  dried. 

Application  :  The  paper  is  used  for  detecting  the 
presence  of  albumin  in  urine.  A  small  piece  im- 
mersed in  the  suspected  fluid  occasions  a  precipitate 
if  albumin  is  present. 


1 82  TEST-PAPERS 

COBALT-  AND   METHYLENE-BLUE 
PAPER 

SULPHIDE  EXCESS  =  Black 

Preparation  :  Paper  is  immersed  in  a  solution  of 
cobaltous  chloride  colored  with  some  methylene 
blue. 

Application  :  Cobalt-  and  mythelene-blue  paper  is 
employed  as  an  indicator  in  estimating  zinc,  copper, 
and  nickel,  by  means  of  sodium  sulphide.  The 
paper  may  also  be  made  so  that  only  one  half  of 
the  strip  is  impregnated  with  the  solution,  the  other 
half  being  left  white.  In  using  this  paper,  a  drop 
of  the  mixture  to  be  tested  for  zinc,  copper,  etc., 
is  placed,  after  the  addition  of  the  sodium  sulphide, 
on  the  white  end  so  that  the  solution  may  diffuse 
to  the  colored  end,  which  will  -be  colored  black  if 
any  excess  of  sulphide  is  present. 

COBALT   PAPER 

SULPHIDE  EXCESS  =  Black 

Synonym :    Stahl's  Paper. 

Preparation  :  Paper  is  impregnated  with  an  almost 
neutral  solution  of  cobaltous  chloride,  representing 
0.3  Gm.  of  CoO  in  100  Gm.  of  solution,  and  then 
dried. 


COLE  IN  PAPER  183 

Application  :  The  paper  is  used  in  the  estimation  of 
zinc  by  means  of  sodium  sulphide;  and  also  for 
hygroscopic  determinations. 

COCHINEAL   PAPER 

ALKALIES  =  Violet  ACIDS  =  Red 

Preparation :  Cochineal  paper  is  prepared  by  im- 
mersing strips  of  good  white  filtering-paper  in  an 
aqueous  cochineal  solution,  and  drying. 

Application :  The  paper  is  used  like  the  tincture. 
Its  sensitiveness  has  been  determined  by  Dieterich 
to  be  such  as  to  indicate  the  presence  of  I  part  of 
sulphuric  acid  and  of  hydrochloric  acid  in  -8000  and 
10,000  parts  of  water,  respectively. 

COLEIN  PAPER 

ALKALIES  =  Yellow  ACIDS  =  Red 

Synonym  :    Boettger's  Test-Paper. 

Preparation :  Cole'in  paper  is  prepared  by  immersing 
sheets  of  filtering-paper  in  an  alcoholic  solution  of 
cole'in,  and  then  drying.  Care  must  be  taken  in  mak- 
ing it,  however,  that  the  color  be  not  too  dark  or 
too  light,  as  on  the  one  hand  it  will  not  be  suffi- 
ciently sensitive,  and  on  the  other  hand  it  will  not 
yield  a  decided  and  sharp  change  of  color.  Paper 
made  too  weak  may  be  remedied  by  immersing  it 
in  water  containing  a  mere  trace  of  ammonia. 


1 84  TEST-PAPERS 

Application  :  Colein  paper  is  said  to  constitute  a  very 
sensitive  indicator  for  titrimetric  determinations. 
It  is  colored  yellow  by  alkalies,  and  red  by  acids. 

The  paper  is  sensitive  to  a  I  :  8000  solution  of 
sulphuric  acid ;  to  1:10000  hydrochloric  acid ;  to 
I  :  8000  potassium  hydrate,  and  to  1:20000  am- 
monia solution. 

CONGO-RED  PAPER 

ALKALIES  =  Red  ACIDS  =  Blue 

Synonyms:   Herzberg's  Paper;   Riegel's  Paper. 

Preparation :  Both  a  red  paper  and  a  blue  are  pre- 
pared for  use.  The  red  paper  is  prepared  by  im- 
pregnating suitable  paper  with  a  solution  obtained 
by  dissolving  I  part  of  Congo  red  in  1000  parts  of 
3O-per-cent.  alcohol.  The  blue  paper  is  obtained 
by  passing  red  paper,  prepared  as  above,  through  a 
faintly  acidulated  bath. 

The  blue  paper  must  be  carefully  preserved,  be- 
cause of  its  tendency  to  become  red.  It  is  al,so 
reddened  by  aniline  and  alkaloids  generally. 

Application  :  The  red  paper  is  useful  for  testing  paper 
for  free  acids,  because  of  its  extreme  sensitiveness 
to  these.  The  paper  may  also  be  used  for  estimat- 
ing organic  bases,  such  as  aniline,  quinine,  brucine, 
morphine,  etc.  It  is  also  serviceable  in  many  cases 
in  which  litmus  and  phenolphtalein  are  useless.  It 
is  not  as  sensitive  as  litmus  paper,  however,  and  is 


CURCUMA    PAPER  185 

of  no  special  value,  except  that  the  dye  adheres 
very  tenaceously  to  the  paper,  and  is  not  washed 
out  readily  on  prolonged  immersion  in  water,  as  is 
the  case  with  litmus  paper. 

The  papers  are  sensitive  to  acids  and  alkalies  to 
the  extent  of  about  I  :  3000. 

CORROSIVE-SUBLIMATE  PAPER 

ARSENIURETTED  HYDROGEN  =  Yellow,  then  Brown 
Synonym:      Fliickiger's  Sublimate  Paper. 

Preparation  :  Paper  is  immersed  in  a  concentrated  so- 
lution of  corrosive  sublimate,  and  dried. 

Application:  Corrosive-sublimate  paper  is  chiefly  em- 
ployed for  the  detection  of  arsenic.  With  arseni- 
uretted  hydrogen  it  affords  a,  at  first  yellow,  then 
brown,  color,  which  is  blackened  by  silver  nitrate. 
The  paper  is  sufficiently  sensitive  to  detect  0.00005 
Gm.  of  arsenous  acid. 

CURCUMA   PAPER 

ALKALIES  =  Brown  ACIDS  =  Yellow 

Preparation  :  Curcuma  paper  is  prepared  by  im- 
pregnating white,  unsized  paper  in  an  alcoholic  solu- 
tion of  curcumin.  It  may  be  prepared  from  the 
root  directly,  also,  but  in  this  case  the  powdered 
root  must  first  be  exhausted  with  water  to  remove  a 
water-soluble  coloring-matter  which  interferes  with 


1 86  TEST-PAPERS 

the  sensitiveness  of  the  color-change;  then  dry- 
ing  the  root  in  the  dark,  and  finally  exhausting 
it  with  alcohol,  the  paper  being  then  imbued  with 
this  solution. 

Tests  :  Curcuma  paper  should  always  be  tested 
before  use  as  to  its  sensitiveness  towards  potassium 
hydrate  and  ammonia.  A  good  paper  will  res- 
pond to  a  1 :  18000  potassium-hydrate  solution, 
and  to  a  1:35  ooo  ammonia  solution. 

Application  :  Curcuma  paper  has  a  yellow  color, 
which  is  changed  to  brown  by  alkalies.  The  paper 
is  useful  for  estimating  alkali  hydrates  and  earths, 
but  is  unsuitable  generally  for  alkalimetry  proper, 
because  the  change  of  color  -  is  scarcely  sharp 
enough.  It  may  be  successfully  used,  however, 
for  titrating  citric,  acetic,  tartaric,  oxalic,  lactic, 
and  succinic  acids  by  means  of  fixed  alkalies,  and 
especially  in  dark  colored  solutions. 

With  ammonia  the  end-reaction  is  indefinite,  and 
only  97$  of  NHS  is  shown  ;  with  ammoniacal  salts, 
a  similarly  indefinite  reaction  is  obtained  ;  hence 
curcuma  paper  is  inapplicable  for  ammonia  or  its 
salts.  The  paper  is  also  unserviceable  for  sodium 
and  potassium  carbonates  and  sulphides,  and  for  a 
similar  reason. 

With  boric,  molybdic,  or  phosphoric  acid,  the 
paper,  after  drying,  is  brown.  Borax,  after  the  ad- 
dition of  an  acid,  yields  a  similar  result,  and  paper 


CURCUMA    PAPER  187 

browned  by  boric  and  hydrochloric  acids  is  colored 
a  handsome  blue  by  alkalies. 

In  silicates  and  borates  of  sodium  and  potassium, 
90$  of  the  combined  alkali  is  shown  in  the  former, 
and  50$  in  the  latter,  the  reactions  being  good. 

Thiosulphates  are  neutral  to  curcuma  paper  ; 
normal  sulphites  and  monophosphates  are  slightly 
alkaline, 

F<;r  fatty  acids,  when  ascertaining  the  saponifica- 
*ion  numbers  of  fats,  oils,  etc.,  the  paper  is  of  no 
value,  because  the  change  of  color  is  not  sharp 
enough,  and  the  soaps  formed  are  distinctly  alkaline 
to  the  paper.  The  paper  is  very  useful,  however, 
for  ascertaining  the  close  of  the  alkaline  reaction  in 
the*  Pettenkofer  process  of  air  analysis. 

Thompson  recommends  also  a  reddish-brown 
paper  obtained  by  impregnating  suitable  paper  with 
an  alcoholic  solution  of  curcumin  or  curcuma  ex- 
tract rendered  alkaline  by  the  addition  of  caustic 
soda.  Paper  so  prepared  becomes  darker  in  color 
on  moistening  with  pure  wate-r,  neutral,  or  alkaline 
solutions,  but  when  immersed  in  an  acid  solution, 
the  immersed  part  becomes  a  bright  yellow,  while 
the  part  outside  of  the  liquid  draws  up  some  of  the 
water  only  from  the  solution  by  capillary  action,  and 
appears  much  darker  by  comparison.  This  paper  is 
very  useful  for  ascertaining  acidity  in  alcohol. 


CAUFORNl*  COUE9I 

of   PHARMACY 


1 8  8  TES  T-PA  PERS 

DIMETHYL-PARAPHENYLENEDIAMINE 
PAPER 

OZONE  =  Bluish-violet 

Synonym  :     Wurster's  Red  Ozone  Paper. 

Preparation:  White,  unsized  paper  is  charged  with  a 
solution  of  dimethyl-paraphenylenediamine,  and 
then  dried. 

Application  :  The  paper  is  employed  for  the  detec- 
tion of  ozone,  sulphuretted  hydrogen,  hydrogen 
dioxide,  turpentine,  colophony,  etc.,  and  also  for 
wood-pulp  in  paper. 

ELDERBERRY    PAPER 

ALKALIES  —  Blue  to  Green  ACIDS  =  Red 

Preparation  :  Elderberry  paper  is  prepared  by  im- 
pregnating filtering-paper  with  the  juice  of  the  el- 
derberry, Sambucus  nigra  L.  and  vS.  canadensis  L. 

Application  :  The  elderberry  paper  is  used  like  geor- 
gina  paper,  though  it  is  somewhat  less  sensitive.  It 
will  react  with  I  part  of  potassium  hydrate  in  5000 
parts  of  water,  and  I  part  of  ammonia  in  10000 
parts  of  water. 


FERROUS-SULPHATE   PAPER 

FERMENT    PAPER 

UREA  =  Brown 

Synonym :    Musculus'  Paper. 

Preparation  :  Ferment  paper  is  prepared  by  filtering 
decomposing  urine  through  white  filtering-paper, 
then  washing  the  latter,  and  coloring  it  with 
turmeric. 

Application :  Ferment  paper  is  applied  for  the  detec- 
tion of  urea,  with  which  it  yields  a  brown  color,  due 
to  the  decomposition  of  the  urea  induced  by  the 
ferment  in  the  paper,  ammonium  carbonate  being 
one  of  the  products  of  the  decomposition  and  af- 
fording the  reaction  with  the  turmeric. 

FERROUS-SULPHATE  PAPER 

HYDROCYANIC  ACID  AND  CYANIDES  =  Blue 

Preparation :  Ferrous-sulphate  paper  is  prepared  by 
impregnating  paper  with  a  solution  of  pure,  crystal- 
lized ferrous  sulphate  and  drying. 

Application:  Ferrous-sulphate  paper  is  applied  for 
the  detection  of  hydrocyanic  acid,  and  for  soluble 
cyanides. 


190  TEST-PAPEKS 

FUCHSINE  PAPER 

AMMONIA  =  Red 

Synonyms  :    Rosanilin  Paper;    Kroupa's  Paper. 

Preparation :  Paper  is  impregnated  with  an  aqueous 
solution  of  fuchsine,  to  which  sufficient  sulphuric 
acid  has  been  added  to  give  the  solution  a  yellowish- 
brown  color.  When  dry,  the  paper  has  a  yellow 
color.  It  must  be  kept  in  well-closed,  glass  vessels. 

Application :  Fuchsine  paper  is  exceedingly  sensitive 
to  gaseous  ammonia,  by  which  it  is  colored  a  car- 
mine red,  the  acid  fuchsine  in  the  paper  becoming 
converted  into  the  neutral  fuchsine.  Kroupa  re- 
ports having  been  enabled  to  detect  0.0005  Gm.  of 
ammonium  chloride  and  0.0005  Gm.  of  ammonium 
carbonate  by  means  of  the  paper. 

Fuchsine   paper  is  also  used  for  the  detection  of 
sulphurous  acid. 

GEORGINA  PAPER 

ALKALIES  =  Green  ACIDS  =  Red 

Synonyms  :    Dahlia  Paper ;   Anthocyanin  Paper. 

Preparation :  Georgina  paper  is  prepared  by  impreg- 
nating unsized  paper  with  an  aqueous  decoction  or 
spirituous  extract  of  the  corollas  of  Georgina 
(Dahlia)  pur  pur  ea  Willdenow.  The  coloring-matter 


GOLD-CHLORIDE   PAPER  IQI 

is    believed     to    be     closely  allied     to    Hoffmann's 
Violet,  and  also  to  anthocyanin. 

Tests  :  Dieterich  estimates  the  paper  to  be  sensitive 
to  sulphuric  acid  1:8000;  to  hydrochloric  acid 
I:  10000;  to  potassa  1:8000;  and  to  ammonia 
i  :  20  ooo. 

Properties  :  The  dry  paper  has  a  handsome,  bluish- 
violet  color.  Should  the  color  be  too  reddish,  as 
may  perhaps  occur,  it  may  be  readily  remedied  by 
immersing  the  paper  in  water  to  which  a  mere  trace 
of  ammonia  has  been  added.  Acids  color  the  paper 
red,  and  alkalies  change  the  color  to  a  handsome 
green,  while  with  concentrated  caustic  alkalies  the 
color  becomes  yellow. 

Cherry    paper,    prepared    from    the  juice  of  red 
cherries,  is  also  used  like  Georgina  paper. 

GOLD-CHLORIDE    PAPER 

OZONE  =  Violet 

Synonym:  Boettger's  Paper;   Ozone  Paper. 

Preparation  :  Paper  is  simply  impregnated  with  a 
neutral  solution  of  gold  trichloride,  and  dried. 

Application :  The  paper  is  applied  for  the  detection 
of  ozone,  by  which  it  is  colored  violet. 


I92  TESl^-PAPERS 


GUAIAC   PAPER 

HALOGENS     r  NITRIC  AND 

AND  OzoNE=Green  or  Blue     -CHROMIC  AciDS=Blue 


Preparation :  White,  unsized  paper  is  impregnated 
with  a  i  :  100  tincture  of  guaiac  resin,  and  dried. 

Application :  Guaiac  paper  is  applied  for  the  detec- 
tion of  ozone,  chlorine,  bromine,  iodine,  nitric  acid, 
and  chromic  acid.  It  is  very  sensitive  to  these,  and 
is  colored  by  them  green  or  blue. 

GUAIAC-   AND   COPPER-SULPHATE 
PAPER 

4 

HYDROCYANIC  ACID  =  Blue 

Synonyms:  Schonbein  and  Pagenstecher's  Test- 
Paper;  Schonbein's  Hydrocyanic-acid  Paper. 

Preparation  :  For  the  preparation  of  guaiac-  and 
copper-sulphate  paper,  a  good  quality  of  white 
filtering-paper  is  first  impregnated  with  a  solution 
of  I  part  of  guaiac  resin  in  100  parts  of  alcohol. 
After  the  paper  has  dried,  it  is  passed  through  a 
solution  of  I  part  of  cupric  sulphate  in  2000  parts 
of  distilled  water,  and  then  dried  again. 

Application  :  The  paper  is  used  for  the  detection  of 
hydrocyanic  acid,  with  the  slightest  traces  of  which 
it  gives  a  blue  color. 


HMMATOXYLIN  PAPER  193 

HAEMATOXYLIN   PAPER 

ALKALIES  =  Blue  ACIDS  =  RED 

Synonym  :   Chevreuil's  Test-Paper. 

Preparation  :  Since  haematoxylin  is  exceedingly  sen- 
sitive to  even  traces  of  calcium  carbonate,  paper  in- 
tended to  be  impregnated  with  it  must  be  previously 
freed  from  these  traces  by  treatment  with  dilute 
hydrochloric  acid,  and  washing  with  distilled  water. 
Paper  so  treated  is  impregnated  with  a  solution  of 
haematoxylin,  or  with  an  extract  prepared,  according 
to  Hager,  by  digesting  10  parts  of  finely  ground 
log-wood  which  had  been  freshly  cut,  with  40  parts 
of  alcohol  and  120  parts  of  distilled  water,  in  a 
stoppered  glass  vessel  for  several  hours.  The 
strained  liquid  is  heated  with  0.7  part  of  potassa 
alum  free  from  iron,  and  7  parts  calcium  chloride 
dissolved  in  a  little  water  acidulated  with  a  few 
drops  of  hydrochloric  acid,  sufficient  to  give  the 
paper  a  faintly  red  color. 

The  paper  may  also  be  prepared  from  an  ex- 
tract made  by  digesting  I  part  of  finely  ground, 
recently  cut  log-wood  in  20  parts  of  distilled 
water,  in  a  well-closed  glass  vessel  for  two  days. 
It  is  important  that  the  log- wood  be  carefully 
selected,  and  that  only  freshly  exposed  sections 
of  the  wood  be  used,  because  both  air  and  light 
affect  it. 


1 94  TES  T-PA  PERS 

Tests:  The  paper  is  sensitive  to  a  I  :  80000-90000 
ammonia,  and  to  1:35  ooo  potassium  hydrate. 

Application  :  The  dried  paper  is  .faintly  yellow  or 
reddish,  on  drying,  and  is  extremely  sensitive  to 
ammonia,  for  which  it  is  used  as  a  very  delicate 
indicator.  It  is  also  serviceable  for  the  fixed  alkalies 
and  for  alkaline  earths  and  mineral  acids,  but  for 
these  it  is  not  as  sensitive  as  litmus. 

The  paper  is  exceedingly  difficult  to  keep  in  good 
condition  on  account  of  its  sensitiveness  to  am- 
monia, traces  even  of  which  suffice  to  change  its 
color  to  blue.  It  must  be  rigorously  preserved, 
hence,  in  an  ammonia-free  atmosphere,  in  well- 
closed,  glass  containers,  and  in  the  dark. 

HOUZEAU'S   OZONE    PAPER 

OZONE  =  Blue 

Preparation :  Houzeau's  ozone  paper  is  prepared  by 
dipping  strips  of  red  litmus  paper  half  way  into  a 
solution  of  potassium  iodide,  and  then  drying. 

Application :  Ozone  acts  on  the  potassium  iodide  in 
the  half  of  the  paper,  and  liberates  the  potassium, 
which  at  once  reacts  with  the  litmus  and  affords  a 
blue  color;  the  other  half  of  the  paper  remains  red, 
of  course.  Sulphurous  acid  does  not  afford  the  re- 
action, but  would  color  the  entire  paper  red,  hence 
any  possible  error  from  this  source  is  eliminated. 


HYACINTH  PAPER  195 

HUCKLEBERRY  PAPER 

ALKALIES  =  Grayish-blue  AciDS  =  Red 

Synonym  :   Uffelman's  Test  Paper. 

Preparation :  Paper  is  immersed  in  a  hydro-alco- 
holic extract  of  huckleberries,  and  then  dried. 
According  to  Uffelmann  an  amyl-alcoholic  ex- 
tract may  also  be  used  for  the  preparation  of  the 
paper. 

Tests  :  The  paper  is  said  to  be  sensitive  to  a 
I  :  6000  potassium-hydrate,  and  to  a  1:15000 
ammonia  solution. 

Application  :  The  paper  is  employed  as  an  indicator 
for  ammonia  and  fixed  alkalies.  The  paper  is  also 
applied  for  the  detection  of  free  hydrochloric 
acid,  which  changes  the  grayish-blue  color  of  the 
paper  to  a  red. 

HYACINTH    PAPER 

AMMONIA  =  Green 
Synonym  :   Selle's  Paper. 

Preparation  :  Hyacinth  paper  is  prepared  by  impreg- 
nating white  filtering-paper  with  a  strong  tincture  of 
blue  hyacinth  flowers. 

Application:  Hyacinth  paper  is  applied  for  the  de- 
tection of  ammonia  va^ars*  which  color  it  green. 


1 96  TES  T-PA  PERS 

INDIGO   PAPER 

CHLORINE  =  Green 

Preparation  :  Filtering-paper  is  impregnated  with  a 
solution  of  indigo. 

Application :  The  paper  is  chiefly  applied  for  the  es- 
timation of  chlorine. 

INDIGO-CARMINE   PAPER 
OXYGEN  =  Yellow  SUGAR  =  Violet  to  Yellow 

Synonym  :    Blue  Carmine  Paper. 

Preparation:  Paper  is  imbued  with  an  aqueous  solu- 
tion of  indigo-carmine. 

Application :  Used  in  the  estimation  of  oxygen ;  and 
also  as  a  test  for  sugar  in  urine. 

INDIGO-CARMINE   AND    SODIUM- 
CARBONATE    PAPERS 

GLUCOSE  =  Colorless  or  Yellowish 

• 

Synonym:    Oliver's  Glucose  Papers. 

Preparation :  Separate  strips  of  filtering-paper  are 
impregnated  respectively  with  solutions  of  indigo- 
carmine  and  of  sodium  carbonate,  and  dried. 

Application  :  The  papers  are  employed  for  the  detec- 
tion of  glucose  in  urine.  By  immersing  a  strip  of 


IR IS  PAPER  ig? 

each  paper  in  the  suspected  fluid,  the  bluish  color 
imparted  to  the  latter  by  the  indigo-carmine  fades 
away  if  glucose  is  present,  due  to  the  reducing 
action  of  the  latter  on  the  indigo-carmine. 

IODATE    PAPER 

SULPHUROUS  ACID  —  Blue 

Preparation:  lodate  paper  is  prepared  by  impregnat- 
ing paper  with  a  solution  prepared  by  heating  2  Gm. 
of  starch  with  100  Cc.  of  water,  and  after  solution, 
adding  0.2  Gm.  of  potassium  iodate  dissolved  in 
5  Cc.  of  water. 

Application :  lodate  paper  may  be  employed  for  the 
detection  of  the  slightest  traces  of  sulphurous  acid, 
which  reduces  the  iodate  present  in  the  paper,  the 
liberated  iodine  then  reacting  with  the  starch  and 
affording  the  well-known  blue  color. 

IRIS   PAPER 

ALKALiESnrGreen       NEUTRAL=Blue       AciDS=:Red 

Synonym  :    Greenwalt's  Paper. 

Preparation:  Iris  paper  is  prepared  by  immersing 
strips  of  filtering-paper  in  a  hot,  aqueous  extract 
of  Iris  versicolor.  Blue  Flag,  and  then  drying  them. 
The  paper  was  recommended  by  Greenwalt  for 
titrimetric  use.  The  neutral  paper  has  a  blue  color, 
changed  to  red  by  acids,  and  to  green  by  alkalies. 


198  TEST-PAPERS 

LACMOID   PAPER 
ALKALIES  =  Blue  ACIDS  =  Red 

Preparation :  Both  a  red  and  a  blue  paper  are  made 
and  used.  The  latter  is  prepared  fro*  a  solution 
made  by  adding  sulphuric  acid  to  an  alcoholic  solu- 
tion of  lacmoid  until  white  paper  shows  a  red  color 
on  impregnation.  If  not  too  much  acid  is  used,  the 
red  paper,  on  drying,  becomes  blue. 

Red  paper  is  made  by  first  treating  the  paper  to 
be  employed  with  dilute  sulphuric  acid  and  drying, 
because  paper  not  so  treated  is  very  prone  to  lose 
its  red  color  and  become  blue.  Just  sufficient  acid 
should  be  used  for  the  paper  to  retain  a  rose-red, 
but  not  darker,  color,  after  several  hours  ;  if  too 
much  acid  has  been  added,  the  sensitiveness  is 
materially  impaired.  The  paper  must  be  very  care- 
fully preserved  in  well-stoppered  bottles,  as  it  is 
very  prone  to  take  on  the  blue  color.  Nor  must  it 
be  handled  much,  as  the  moisture  of  the  hand  suf- 
fices to  color  it  blue. 

Application  :  Blue  lacmoid  paper  is  very  useful  for 
application  by  lamp-  or  gas-light,  as  a  pure  blue  color 
is  observed,  whereas  with  litmus  paper  the  color 
appears  more  or  less  violet.  This  paper  is  about 
equal  in  value  to  litmus  paper,  but  the  red  lacmoid 
is  more  sensitive  than  the  corresponding  litmus 


LA  CM O ID    PAPER  199 

paper,    the  change  of    color  being    much  sharper, 
and  the  blue  brighter. 

A  great  advantage  possessed  by  the  lacmoid 
papers  is  the  tenacity  with  which  the  color  is  retained 
on  prolonged  contact  with  water. 

The  papers  are  very  useful  for  titrations  in  cold 
and  in  colored  liquids.  The  red  paper  indicates  at 
the  end  of  the  reaction  the  slightest  trace  of  alkali, 
and  even  if  the  liquid  is  impregnated  with  carbonic- 
acid  gas ;  the  blue  paper,  on  the  other  hand,  shows 
only  a  faint  red  in  the  presence  of  traces  of  alkali, 
if  free  carbonic-acid  gas  is  present,  and  the  redness 
disappears  on  exposure  to  the  air  for  a  few  mo- 
ments. 

Sulphides  of  the  alkalies  may  be  sharply  titrated 
with  lacmoid  paper,  whereas  the  lacmoid  solution 
is  decolorized  by  the  liberated  hydrogen  sulphide. 
The  paper  is  also  useful  for  testing  for  the  presence 
of  neutral  chromates,  or  chromic  acid  in  the  presence 
of  bichromates.  It  can  also  be  used  for  the  alkali 
carbonates  and  sulphites,  with  which  lacmoid  solu- 
tion cannot  be  used.  It  is  also  applicable  for  esti- 
mating the  bases  in  the  borates  of  the  alkalies  and 
alkaline  earths,  and  also  in  silicates  of  the  al- 
kalies. The  total  alkali  of  arsenites  may  also  be 
sharply  titrated,  since  arsenous  acid  is  neutral  to 
the  paper. 


260  TES  T-PA  PERS 

LEAD  PAPER 

SULPHIDES  =  Black 

Preparation  :  White,  unsized  paper  is  dipped  in  a  10- 
per- cent,  solution  of  lead  acetate  in  distilled  water, 
and  dried  in  an  atmosphere  free  from  hydrogen  sul- 
phide. The  paper  must  be  very  carefully  preserved 
in  an  atmosphere  free  from  this  gas,  and  preferably 
in  glass-stoppered  bottles. 

Application:  The  paper  is  applied  to  the  detection  of 
hydrogen  sulphide  and  alkali  sulphides. 

LITMUS  PAPER 
ALKALlES=Blue       NEUTRAL^Violet      AciDS=Red 

Of  litmus  papers,  three  kinds  are  to  be  met  with — a 
red,  blue,  and  violet,  the  last  being  a  neutral  paper. 
The  best  paper  only  should  be  employed  in  making 
them,  and  should  be,  preferably,  not  too  thin,  and 
of  firm  texture,  because  much  better  results  are  ob- 
tained with  a  paper  not  too  porous,  the  reason  be- 
ing that,  on  moistening,  if  the  paper  is  too  bibu- 
lous, the  liquid  diffuses  over  too  great  a  surface, 
and  thus  materially  weakens  the  reaction,  whereas 
if  the  solution  applied  remains  on  the  spot  where 
placed,  its  full  acidity  or  alkalinity  is  exerted  on 
the  one  spot.  This  fact  also  holds  good  for  all 
papers. 


LITMUS  PAPER  2OI 

Preparation  :  Blue  Litmus  Paper  is  prepared  by  im- 
pregnating a  good  quality  of  white,  unsized  paper 
with  blue  litmus  solution  (see  page  102),  and  dry- 
ing. It  is  best  preserved  in  a  jar,  in  the  bottom  of 
which  is  placed  a  small  lump  of  ammonium  carbon- 
ate. 

Red  Litmus  Paper  is  prepared  by  immersing  the 
blue  paper  in  water  faintly  acidulated  with  hydro- 
chloric acid,  and  then  drying  in  an  ammonia-free 
atmosphere.  The  paper  should  be  preserved  in  a 
jar  in  which  is  placed  a  small  quantity  of  cotton 
moistened  with  a  few  drops  of  acetic  acid. 

Neutral  Litmus  Paper  is  prepared  by  impregnat- 
ing a  pure  paper  with  a  perfectly  neutral  litmus  so- 
lution. The  paper  has  a  light  reddish-violet  tint, 
and  is  very  sensitive  to  either  acids  or  alkalies.  Care 
must  be  taken  that  the  paper  be  rather  red  than 
violet  when  moist,  because  on  drying  the  paper  is 
apt  to  acquire  a  blue  color  if  the  moist  paper  be 
violet.  The  dry  paper  must  be  very  carefully  pre- 
served in  small,  well-stoppered  bottles,  and  must 
be  carefully  protected  from  acid  or  ammoniacal 
vapors,  otherwise  it  rapidly  loses  its  extreme  sen- 
sitiveness. 

Tests:  Carefully  made-blue  litmus  paper  is  sensitive 
to  i  :  60  ooo  sulphuric  acid  solution,  and  to  a 
I  :  80  ooo  hydrochloric-acid  solution.  The  red 
paper  is  sensitive  to  a  I  :  50000  potassa  solution, 
and  to  a  1 :  80  ooo  solution  of  ammonia. 


202  TEST-PAPERS 

Application  :  Litmus  paper  is  very  serviceable  for  de- 
tecting the  acidity  or  alkalinity  of  solutions.  It  is 
also  applicable  for  titrations  in  hot  or  cold  liquids, 
and  also  when  the  titrated  solutions  are  cloudy. 
Even  when  carbonic-acid  gas  is  present,  the  paper 
is  applicable,  because  the  gas  is  rapidly  dissipated 
from  the  paper,  and  the  end  reaction  may  hence  be 
easily  observed. 

MALLOW   PAPER 

ALKALIES  =  Bluish-green  ACIDS  =  Red 

Synonyms:  Hollyhock  Paper;  Althaea  Paper;  Stev- 
enin's  Paper. 

Preparation :  Mallow  paper  is  prepared  by  impreg- 
nating white  filtering-paper  with  an  extract  prepared 
by  macerating  20  parts  of  flowers  of  Althcea  rosea 
in  a  mixture  of  900  parts  of  alcohol,  100  parts  of 
water,  and  I  part  of  ammonia,  expressing  after  a 
week,  and  filtering. 

Application  :  The  prepared  paper  has  a  purplish-blue 
color,  and  is  applied  as  a  test  for  acids  and  alkalies ; 
the  former  change  its  color  to  red,  and  the  latter  to 
bluish-green.  It  is  more  sensitive  than  georgina 
paper  to  acids. 

The  paper  may  be  applied  for  the  detection  of 
nitrites  in  potable  waters.  It  is  colored  purple  by 
traces.  Its  sensitiveness,  according  to  Dieterich,  is 


METAPHENYLENEDIAMINE   PAPER  20} 

as  follows:  Sulphuric  acid,  I  :  10000;  hydrochloric 
acid,  1:13  ooo;  potassium  hydrate,  i  :  8ooo;  and 
ammonia,  1 :  20  ooo. 

MANGANOUS-CHLORIDE   PAPER 

Preparation  :  Filter-paper  is  impregnated  with  a 
solution  of  manganous  chloride,  MnCl,  +  4H9O, 
and  dried. 

Application  :  This  paper  shows  the  presence  of 
nascent  oxygen  on  moistening  with  soda  lye. 

MANGANOUS-ACETATE   PAPER 

Preparation  :  Paper  is  immersed  in  a  solution  of 
manganous  acetate,  and  dried. 

Application  :  The  paper  is  applied  for  the  detection 
of  traces  of  ozone. 

METAPHENYLENEDIAMINE    PAPER 

NITRITES  =  Yellowish-brown 

Synonym:   Griess's  Yellow  Test-Paper. 

Preparation  :  The  paper  is  prepared  by  impregnating 
white,  unsized  paper  with  an  alcoholic  solution  of 
metaphenylenediamine,  and  then  drying.  At  times, 
sulphanilic  acid  is  also  added  to  the  solution  before 
the  immersion  of  the  paper. 


204  TES  T-PA  PERS 

Application:  Metaphenylenediamine  paper  is  an 
exceedingly  delicate  test  for  nitrous  acid  and  ni- 
trites, by  which  it  is  colored  yellowish-brown. 

METHYL-ORANGE   PAPER 

ALKALIES  =  Yellow     ACIDS  =  Deep  Brownish-yellow 
Synonyms:    Helianthin  Paper;    Tropaeolin  D,  Paper. 

Preparation :  Paper  is  impregnated  with  an  aqueous 
solution  of  methyl  orange  and  then  dried. 

Application:  Methyl-orange  paper  is  applied  as  an 
indicator  in  the  estimation  of  both  acids  and  alkalies. 
By  the  latter  it  is  colored  yellow ;  by  the  former  a 
deep,  brownish-yellow.  The  paper  will  show  I  part 
of  sulphuric  acid  in  10,000  parts  of  water,  and  I  part 
of  hydrochloric  acid  in  15,000  parts  of  solution. 

OENOKRINE    PAPER 

Preparation  :  Oenokrine  paper,  introduced  in  Paris 
for  determining  the  nature  of  foreign  coloring- 
matters  in  red  wine,  is  prepared,  according  to  Julius 
Miiller,  by  impregnating  paper  with  a  solution  of 
lead  acetate,  and  drying. 

Application :  On  immersing  the  prepared  paper  in 
genuine  red  wine,  allowing  to  drip,  and  then  spread- 
ing on  a  sheet  of  white  paper,  the  test-paper  on 
drying  shows  a  grayish-blue  color.  With  huckle- 
berry extract,  it  yields  a  similar  color.  If  fuchsin 


PALLADIOUS  CHLORIDE  PAPER  205 

has  been  added  to  the  wine,  a  fine  red  color  is  ob- 
tained. With  the  coloring-matters  of  mallow  and 
log-wood,  a  blue  color  results.  Ammoniacal  carmine 
or  cochineal  solution  present  in  the  wine  will  yield 
a  pale  violet.  Extract  of  Pernambuco  wood  affords 
a  dirty  yellow.  With  indigo,  the  paper  shows  a 
deep  blue. 

Oenokrine  paper  is  not,  however,  reliable. 


PALLADIOUS-CHLORIDE   PAPER 

REDUCING  GASES  =  Black 

Synonym:   Merget's  Paper. 

Preparation  :  Paper  is  impregnated  with  a  solution  of 
palladious  chloride,  PdCl, ,  of  such  strength  that 
every  100  Cc.  of  solution  represents  5  Gm.  of 
metallic  Pd.  A  solution  of  I  part  of  sodium  and 
palladium  chloride,  PdCla  +  2NaCl,  in  12  parts  of 
distilled  water  may  also  be  used  for  the  purpose, 
instead. 

Application:  The  paper  is  employed  for  detecting 
carbon  monoxide,  hydrogen-sulphide,  ozone,  methane, 
ethane  and  illuminating  gas,  which  precipitate  me- 
tallic palladium. 

Paper  impregnated  with  palladious  chloride  and 
mercuric  chloride  is  also  used  for  similar  purposes. 
It  is  known  as  Merget's  paper. 


206  TEST-PAPERS 

PHENOLPHTALEIN   PAPER 

ALKALIES  =  Red  ACIDS  =  Colorless 

Preparation:  In  making  phenolphtalein  paper,  only 
the  finest  quality  of  paper  should  be  used.  The 
paper  is  simply  dipped  into  an  alcoholic  phenol- 
phtalein solution,  and  then  dried. 

Application :  The  paper  may  be  applied  in  great 
measure  like  the  solution.  It  is  unaffected  by  am- 
moniacal  vapors  or  solutions,  or  by  solutions  of  the 
carbonates  of  the  alkalies.  It  has  been  recommended 
as  being  useful  for  determining  the  comparative 
quantities  of  carbon  dioxide  in  the  atmosphere  of 
schoolrooms,  factories,  hospitals,  etc.,  because  of 
its  property  of  losing  the  redness  caused  by  mois- 
tening with  a  drop  of  lime-water,  when  carbon 
dioxide  is  present  in  the  air;  the  greater  the  quan- 
tity present,  the  more  rapidly  does  the  color  fade. 
The  paper  is  sensitive  to  a  1:20000  potassium- 
hydrate  solution. 

PHLOROGLUCIN-VANILLIN   PAPER 

HYDROCHLORIC  ACID  =  Red  LIGNIN  =  Red 

Synonym:  Guenzburg's  Test-Paper. 

Preparation:  Paper  is  immersed  in  a  solution  of 
I  part  of  phloroglucin  and  2  parts  of  vanillin  in  30 
parts  of  alcohol,  and  then  dried. 


POLE-jREAGENT  PAPER  2O? 

Application:  The  paper  is  at  times  employed  instead 
of  Guenzburg's  solution  for  the  detection  of  free 
hydrochloric  acid  in  gastric  juice.  It  is  also  used 
for  the  detection  of  lignin  in  paper. 


PICRO-CITRIC-ACID   PAPER 

ALBUMIN  =  Precipitate 

Synonym  :  Oliver's  Albumin  Paper. 

Preparation  :  Paper  is  impregnated  with  a  concen- 
trated aqueous  solution  of  picric  and  citric  acids, 
and  then  dried. 

Application :  The  paper  is  employed  for  detecting 
albumin  in  urine,  by  immersing  a  piece  of  the  paper 
and  stirring.  If  albumin  is  present,  a  precipitate  is 
formed. 

POLE-REAGENT  PAPER 

NEGATIVE  CURRENT  =  Red 

Preparation :  Paper  is  impregnated  with  a  dilute  al- 
coholic solution  of  phenolphtalein  and  sodmm  sul- 
phate, and  dried. 

Application :  This  paper  is  employed  for  the  recog- 
nition of  the  negative  poles  of  batteries,  the  paper 
being  reddened  by  a  negative  electrical  current. 


208  TEST-PAPERS 

POTASSIO-MERCURIC-IODIDE  PAPER 

ALBUMIN  =  Precipitate 

Synonym:   Hoffmann's  Albumin  Paper. 

Preparation :  A  solution  is  prepared  by  dissolving  i 
part  of  potassium  iodide  in  2  parts  of  water,  and 
adding  this  to  a  solution  of  I  part  of  mercuric 
chloride  in  20  parts  of  water.  Filtering-paper  is 
dipped  into  the  mixture  and  then  dried. 

Application  :  Hoffmann's  test-paper  is  applied  for  the 
detection  of  albumin  in  urine,  by  dipping  a  piece  of 
the  paper  into  the  suspected  urine,  which  has 
been  previously  acidified  with  a  few  drops  of  acetic 
acid.  A  precipitate  denotes  the  presence  of  al- 
bumin. 

POTASSIUM-CHROMATE   PAPER 

LEAD  SALTS  =  Yellow  SILVER  SALTS  =  Red 

Preparation :  Filter-paper  is  impregnated  with  a 
i  :  250  solution  of  potassium  chromate,  and  dried. 

Application  :  Potassium-chromate  paper  is  applied 
for  the  detection  of  lead  and  silver  salts.  It  will 
show  the  presence  of  I  part  of  lead  acetate  in  2000 
parts  of  water,  the  paper  becoming  a  bright  yellow 
from  the  formation  of  lead  chromate.  With  silver 
nitrate  it  will  give  a  fine  red  color,  due  to  silver 


POTASSIUM-FERROCYANIDE  PAPER  209 

chromate  being  formed,  and  it  will  show  the  pres- 
ence of  I  part  of  the  nitrate  in  3000  parts  of  so- 
lution. 


POTASSIUM-FERRICYANIDE  PAPER 

FERROUS  SALTS  =  Blue 

Preparation:  Filtering-paper  is  immersed  in  a  I  :  250 
solution  of  potassium  ferricyanide,  and  then  dried. 

Application:  The  paper  is  applied  for  the  detection  of 
ferrous  salts,  with  which  it  yields  a  blue  color.  It 
will  detect  I  part  of  ferrous  sulphate  in  40000 
parts  of  solution. 

POTASSIUM-FERROCYANIDE   PAPER 

FERRIC  SALTS  =  Blue  CUPRIC  SALTS  =  Red 

Preparation :  Filtering-paper  is  impregnated  with  a 
1:250  solution  of  potassium  ferrocyanide,  and 
dried. 

Application  :  Potassium-ferrocyanide  paper  is  applied 
for  the  detection  of  ferric  and  cupric  salts,  with 
which  it  yields  a  blue  and  red  color  respectively. 
It  will  detect  I  part  of  ferric  chloride  in  2500  of 
solution,  and  I  part  of  cupric  sulphate  in  2000  of 
solution. 


2 1 0  TES  T-PA  PERS 

POTASSIUM-IODIDE   PAPER 

LEAD=Yellow         BlSMUTH:=  Black         SiLVER=Red 

Preparation:  Pure  white  filtering-paper  is  impreg- 
nated with  a  1 :  250  solution  of  potassium  iodide, 

Application :  Potassium-iodide  paper  is  used  for  the 
detection  of  various  metals,  such  as  lead,  bismuth, 
silver,  etc.  It  will  show  the  presence  of  I  part  of 
lead  acetate  in  500  of  solution ;  I  part  of  bismuth 
nitrate  in  7000  parts  of  solution ;  and  I  part  of 
silver  nitrate  in  1000  parts  of  solution 

POTASSIUM-IODIDE   AND   STARCH 
PAPER 

OXIDIZERS  =  Blue 

Synonym  :   Schonbein's  Ozone  Paper. 

Preparation:  White  filtering-paper  is  impregnated 
with  a  solution  prepared  from  10  parts  of  starch, 
200  parts  of  water,  and  I  part  of  potassium  iodide. 
The  dried  paper  must  be  preserved  as  carefully  as 
possible  from  prolonged  contact  with  air. 

Application :  The  paper  is  applied  for  the  detection 
of  oxidizers,  such  as  chlorine,  iodine,  bromine, 
nitrous  acid,  and  ozone,  etc.,  by  which  it  is  colored 
blue. 

The  paper  will  detect  I  part  of  chlorine  in  30,000 
parts  of  water. 


RESAZURIN  PAPER  211 


POTASSIUM-SULPHOCYANATE   PAPER 

FREE  HYDRO-    ~  ,    ,  FERRIC 

CHLORIC 


Preparation  :  Potassium-sulphocyanate  paper  is  pre- 
pared by  immersing  paper  in  a  lo-per-cent.  solution 
of  potassium-sulphocyanate  to  which  a  little  ferric- 
acetate  solution  has  been  added. 

Application  :  The  paper  is  applied  according  to  Mohr 
for  the  detection  of  free  hydrochloric  acid  in  gastric 
juice. 

A  paper  prepared  without  the  addition  of  the 
ferric  salt  is  applied  for  the  detection  of  ferric 
chloride,  with  which  it  yields  a  blood-red  color. 
Its  sensitiveness  to  the  iron  salt  is  such  as  to  detect 
I  part  of  the  salt  in  5000  parts  of  solution. 

RESAZURIN   PAPER 

ALKALIES  =  Blue  ACIDS  =  Red' 

Synonyms:  Diazoresorcin  Paper;  Azoresorcin  Paper; 
Weselsky's  Paper. 

Preparation:  Resazurin  paper  is  prepared  by  im- 
pregnating unsized  paper  with  a  solution  of  resazurin 
made  as  directed  under  "  Resazurin,"  and  then 
drying. 

Application:  Resazurin  paper  can  only  be  used  when 


212  TEST-PAPERS 

very  recently  prepared,  because  the  resazurin  under- 
goes reduction,  becoming  converted  into  resorufm. 
With  alkalies  the  color  of  the  paper  is  blue;  acids 
change  the  color  to  red. 


RHUBARB   PAPER 

ALKALIES  =  Red  ACIDS  =  Yellow 

Preparation:  A  red  and  a  yellow  rhubarb  paper  may 
be  made. 

Yellow  Rhubarb  Paper  is  obtained  by  impregnat- 
ing white  filtering  paper  in  an  alcoholic  extract  of 
the  rhubarb  root,  then  passing  through  water 
faintly  acidulated  with  phosphoric  acid,  and  finally 
drying. 

Red  Rhubarb  Paper  is  obtained  by  passing  the 
paper,  after  impregnation  with  the  rhubarb  ex- 
tract, through  water  rendered  alkaline  with  am- 
monia. 

Application  :  The  yellow  paper  yields  a  fine  red  color 
with  alkalies,  whereas  the  red  paper  is  changed  to 
yellow  by  acids.  The  yellow  paper  is  stated  by 
Dieterich  to  be^  sensitive  enough -to  detect  I  part  of 
potassium  hydrate  in  8000  of  water;  and  I  part  of 
ammonia  in  20,000  parts  of  water.  The  paper  is 
unaffected  by  boric  acid. 


SCHIFF'S  PAPER  213 

ROSE    PAPER 

ALKALIES  =  Bright-green  ACIDS  =  Pink 

Preparation:  Rose  paper  is  prepared  by  dipping 
paper  into  an  infusion  of  the  petals  of  the  red  rose 
(Rosa  gallica),  and  drying. 

Application:  Rose  paper  is  but  little  used,  and  pos- 
sesses no  advantage  over  other  test-papers.  The 
paper  is  colored  a  bright-green  by  alkalies,  and  by 
acids  a  pink. 

ROSOLIC-ACID    PAPER 

ALKALIES^  Red  ACIDS  =  Yellow 

Preparation  :  Rosolic-acid  paper  is  prepared  by  im- 
pregnating filtering-paper  with  a  i-per-cent.  solution 
in  6o-per-cent.  alcohol. 

Application :  The  paper  has  a  yellow  color,  and  is  ap- 
plicable to  all  purposes  as  the  rosolic-acid  test  solu- 
tion. It  is  sensitive  to  a  I  :  20000  potassium- 
hydrate  solution. 

SCHIFF'S   PAPER 

GLUCOSE  AND  CARBOHYDRATES  =  Red 

Preparation :  SchifFs  paper  is  prepared  by  immersing 
strips  of  filtering-paper  in  a  mixture  of  equal  vol- 
umes of  glacial  acetic 'acid  and  xylene,  and  a  very 
little  alcohol. 


214  TES  T-PA  PERS 

Application  :  Schiff's  paper  is  applied  for  the  detection 
of  glucose  and  other  carbohydrates.  The  substance 
to  be  tested  is  heated  with  sulphuric  acid,  and  if 
carbohydrates  are  present,  furfurol  is  evolved  and 
colors  the  test-paper  held  in  the  vapors  a  fine  red. 

SERUM    PAPER 
Synonym :    Richardson's  Paper. 

Preparation :  Serum  paper  is  prepared  by  impreg- 
nating filtering-paper  with  serum  obtained  from  a 
typhoid-fever  subject,  and  then  drying  carefully  in 
an  unwarmed  place. 

Application:  Serum  paper  is  used  instead  of  fresh 
typhoid  serum  for  carrying  out  Widal's  typhoid 
reaction. 

SILVER-NITRATE    PAPER 

PHOSPHORUS  =  Black  ARSENIC  =  Yellow 

CHROMATES  =  Red  URIC  ACID  =  Brown 

Synonym:   Schiff's  Paper. 

Preparation :  Fitter-paper  is  impregnated  with  a  solu- 
tion of  silver  nitrate,  and  dried  in  air  free  from  hy- 
drogen sulphide. 

Application :  Silver-nitrate  paper  is  employed  for  the 
detection  of  chromic  and  arsenous  acids,  and  for 
detecting  phosphorus,  by  the  vapors  of  which  it  is 
blackened.  It  is  an  exceedingly  sensitive  means  of 
detecting  arsenic. 

Silver-nitrate  paper  is  also  used  for  detectiug  uric 


STARCH-  AND  A  MMONIUM-PER  SULPHA  TE  PAPER  2 1 5 

acid  in  urine.     The  paper  is  stained  brown  by  uric 
acid. 

STARCH    PAPER 

IODINE  =  Blue 

Preparation:  Starch  paper  is  prepared  by  applying 
with  a  broad,  camel's-hair  brush  a  solution  ob- 
tained by  triturating  10  parts  of  starch  with  10 
parts  of  cold  water,  and  then  adding  890  parts  of 
boiling  water.  Care  should  be  taken  that  no  spot 
on  the  paper  be  touched  twice,  otherwise  fibers  of 
the  paper  are  carried  off  mechanically.  The  paper 
should  be  dried  in  an  unwarmed  place. 

Application :  Starch  paper  is  exceedingly  sensitive  to 
traces  of  free  iodine,  with  which  it  strikes  a  blue 
color  owing  to  the  formation  of  starch  iodide.  One 
part  of  iodine  in  25000  may  be  detected  by  means 
of  this  paper. 

STARCH-    AND    AMMONIUM-PERSUL- 
PHATE   PAPER 

IODIDES  =  Intensely  Blue 

Preparation:  According  to  Bourget,  filtering-paper  is 
impregnated  with  a  5-per-cent.  starch  solution, 
dried,  and  then  cut  up  into  squares  of  5  Cm.  each. 
Two  or  three  drops  of  a  5-per-cent.  ammonium-per- 
sulphate solution  are  dropped  in  the  center  of  each 
square,  and  the  pieces  dried  in  the  dark. 


2l6  TEST  PAPERS 

Application :  Paper  so  prepared,  and  immersed  in  a 
fluid  containing  even  traces  of  iodine,  develops  an 
intensely  blue  color,  a  distinct  reaction  being  visible 
in  solutions  containing  0.00005  per  cent,  of  potas- 
sium iodide.  Paper  prepared  with  sodium-  or  po- 
tassium-persulphate may  also  be  used,  but  is  de- 
cidedly less  sensitive.  Bourget  recommends  the 
paper  especially  for  the  investigation  of  saliva  and 
urine  at  the  bedside. 

SULPHANILIC-ACID   AND   ALPHA-NAPH- 
TYLAMINE-SULPHATE   PAPER 

NITRITES  =  Red 

Synonym :  Griess's  Red  Test-Paper. 

Preparation :  White,  unsized  paper  is  impregnated 
with  an  alcoholic  solution  of  sulphanilic  acid  and 
alpha-naphtylamine  sulphate  (or  hydrochlorate), 
and  dried. 

Application :  The  paper  is  employed  in  the  detection 
of  nitrous  acid  and  nitrites,  which  change  the  color 
of  the  paper  to  a  deep  red.  It  is  also  used  to  detect 
bilirubin  and  aldehydes,  in  urine. 

TANNIN   PAPER 

ALKALIES  =  Brown  FERRIC  SALTS  —  Black 

Preparation :  Tannin  paper  is  prepared  by  immersing 
filter-paper  in  a  concentrated  solution  of  tannin, 
and  drying  in  a  warm  place. 


THALLOUS-HYDRATE  PAPER  21? 

Application:  Tannin  paper  is  employed  for  caustic 
alkalies,  alkaline  earths,  ammoniacal  salts,  and  iron 
salts. 

TETRAMETHYL-PARAPHENYLENEDI- 
AMINE   PAPER 

OZONE  —  Violet 

Synonyms:  Wurster's  Blue  Ozone  Paper;  Tetra  Paper. 

Preparation  :  White,  unsized  paper  is  impregnated 
with  a  solution  of  tetramethyl-paraphenylenedia- 
mine,  and  dried. 

Application:  The  paper  is  employed  for  detecting 
ozone  and  ozonizers,  as  turpentine,  pine  wood,  and 
also  hydrogen  dioxide.  Traces  of  ozone  or  nascent 
oxygen  in  neutral  or  acetic-acid  solutions  color  the 
paper  intensely  violet  or  bluish-violet. 

THALLOUS-HYDRATE    PAPER 

OZONE  ^  Brown 

Synonyms:  Boettger's  Ozone  Paper;  Thallium- 
Hydroxide  Paper. 

Preparation:  Paper  is  impregnated  with  a  lo-per-cent. 
solution  of  thallous  hydrate  recently  prepared  by 
precipitating  a  solution  of  thallous  sulphate  by  the 
proper  stoichiometrical  quantity  of  baryta  water. 
The  paper  should  be  rapidly  dried,  and  is  colorless. 


2 1 8  TES  T-PA  PERS 

Application:  The  paper  is  applied  for  the  detection 
of  ozone,  which  colors  it  brown  from  the  formation 
of  thallium  oxide.  The  absence  of  nitrous  acid 
must  be,  however,  assured,  as  this  may  partly,  or 
even  entirely,  prevent  the  reaction. 

TROP^EOLIN   PAPER 

ALKALIES  =  Yellow  ACIDS  =  Red 

Synonyms:    Boas'  Paper;    Lutke's  Paper. 

Preparation :  Tropseolin  paper  is  prepared  by  dipping 
white  filtering-paper  in  a  I  :  1000  solution  of  tro- 
paeolin  OO  and  then  drying. 

Application :  The  paper  may  be  applied  like  tro- 
paeolin-OO  solution.  It  is  reddened  by  free  acids, 
and  the  yellow  color  is  restored  by  alkalies.  It  is 
excellent  for  oxalic  and  organic  acids,  and  is  not 
affected  by  carbonic-acid  gas,  bicarbonates,  or  acid 
salts. 

ULTRAMARINE  PAPER 

ACIDS  =  Colorless 

Preparation:  A  convenient  quantity  of  ultramarine 
is  carefully  washed  with  water,  and  then  mixed 
with  a  decoction  of  Irish  moss  in  water  (i  :  30  or 
40).  The  mixture  so  obtained  is  then  painted  on 
unsized  paper  as  evenly  and  thinly  as  possible,  by 
means  of  a  flat  brush. 


ZINC-IODIDE   AND    STARCH  PAPER  21$ 

Application:  Ultramarine  paper  is  applied  for  the 
detection  of  free  acids  in  alum,  aluminum  sul- 
phate, etc.  The  acids  decolorize  the  paper. 

WHITE-LEAD    PAPER 

METALLIC  SALTS  =  Color  of  Sulphides 

Synonyms  :    Schott's  Paper;    Polka  Paper. 

Preparation :  The  paper  is  prepared  by  coating  sized 
paper  with  a  mixture  of  white  lead  and  starch 
paste. 

Application  :  White-lead  paper  is  used  as  an  indicator 
in  titrating  solutions  of  metallic  salts  with  sodium 
sulphide. 

ZINC-IODIDE   AND   STARCH    PAPER 

IODINE  =  Blue 

Preparation :  Paper  is  impregnated  with  the  solution 
prepared  as  detailed  under  Zinc-Iodide  and  Starch, 
and  dried. 

Application :  The  paper  is  sometimes  employed  in 
iodimetric  determinations.  It  is  rendered  blue  by 
traces  of  free  iodine. 


PART  IV 
TABLES  AND  TABULAR  SUMMARY 


H.  TROMMSDORFF'S  TABLE,  SHOWING  THE  SENSITIVENESS  OF 
INDICATORS  TO  ACIDS  AND  ALKALIES 


Indicators 

Strength  of 
Indicator 
Solution 

Cc.of 
Indicator 
Solution 
added  to 
ioo  Cc.  of 
titrated 
Fluid 

Cc.  of  titrating  Fluid  required 

Azolitmin  .... 

i  :  loo  water 

0.5 

1.2—  HC1  ;  3—  KOH 

IOO                       IOO 

Carminic  acid 

1:100  water 

0-5 

0.7—  HC1;    0.8—  NH,  ; 

100                             IOO 

1.2—  NaOH 

IOO 

Cochineal.  .  .  . 

1:80  water 

0.5 

3—  HC1;     2.8—  NaOH 

IOO                             IOO 

Congo  red.  .  .  . 

1:100,  30/6- 
alcohol 

O.I 

0.7—  HC1;     0.6—  NH,  ; 

'  IOO                             IOO 

2.5—  KOH 

IOO 

Corallin     .... 

I  "ioo  water 

Oe 

o  6    H  HC1  •     o  8    n  NH    • 

IOO                             IOO 

2.8—  NaOH 

IOO 

220 


TABLES  AND    TABULAR   SUMMARY 
H.  TROMMSDORFF'S  T ABLE- Continued 


221 


Indicators 

Strength  of 
Indicator 
Solution 

Cc.  of 

Indicator 
Solution 
added  to 
100  Cc.  of 
titrated 
Fluid 

Cc.  of  titrating  Fluid  required 

Ethyl  orange. 

1:400,  30$- 
alcohol 

0.2 

^HC1 

Fluorescein  .  . 

1:100  alco- 
hol 

O.I 

Fluorescence    neutralized    by 
0.5  —  HC1 

10 

Gallein    (com- 
mercial). ... 

1:2  alcohol 

O.I 

1.2  —  HC1  brownish; 

IOO 

1.6—  -NH3  violet. 

IOO 

• 

1.2  HC1    to   last  restores 

IOO 

color,    which     is     changed 
again  by  0.7  —  KOH 

Litmus    (puri- 
fied)... 

i  :io  water 

O.2 

0.05  —  HC1-    o.i  —KOH 

Methyl  orange 

1:200  water 

i  0.05  j 
Jo.i    I 

(0.2      \ 

10                             10 

i  HC1  ;  restored  by 

IOO 

0.9  NHs  ;  again   acid   by 

I  —  HC1,  and    restored    by 

IOO 

i  KOH  ;  quantity  of  in- 

100 

dicator  immaterial 

Orange-peel 
tincture.  .  .  . 

1:5  water 

I 

o.i  -KOH 

10 

Phenacetolin. 

1:200  alco- 
hol 

(    O.I 
(    0.2 

o.i  —KOH  :  with  0.2  Cc.  the 
10 
change  is  more  distinct 

222 


TABLES  AND    TABULAR  SUMMARY 
H.  TROMMSDORFF'S 


Indicators 


Strength  of 
Indicator 
Solution 


Cc.  of 

Indicator 

Solution 

added  to 

100  Cc.  of 

titrated 

Fluid 


Cc.  of  titrating  Fluid  required 


Phenolphtal- 
ein .  • 


Poirrier  blue, 
C4B 


1:100  alco- 
hol 


1:200  water 


o.5 


O.I 


Rosolic  acid. . 


Tropaeolin 


alcohol 


1:400,  30$- 
alcohol 


0.5 


O.2 


0.5  — KOH  necessary  for  dis- 
100 

tinct  redness 


0.7 KOH     colorless     when 

100 

titrated    hot  ;    restored    by 

1.2 HC1  to  violet 

100 


0.7—  HC1;     0.8—  NH3 


100 


2.5  -HC1 
10 


100 

4.1—  KOH 
100 


TABLES  AND    7*ABULAR   SUMMARY 


223 


R.  T.  THOMSON'S  TABLE,  SHOWING  THE  HYDROGEN  ATOMS 
REPLACED  BY  NAOH  OR  KOH  WHEN  A  COMPOUND  NEUTRAL 
TO  THE  INDICATOR  IS  FORMED.  THE  BLANK  SPACES  INDI- 
CATE THAT  THE  END-REACTION  IS  OBSCURE 


Acid 

Formula 

Methyl 
Orange 

Phenolphtalein 

Litmus 

Cold 

Cold 

Boiling 

Cold 

Boiling 

HaS04 
HC1 
HNO, 
H2S203 
HaC03 
HaSO, 
HaS 
H,P04 
H3AsO4 
H3As03 
HN02 
H4Si04 
H3B03 
H2CrO4 
HaC204 
HCaH3O2 
HC4H7O2 
H2C4H404 
HC3H603 
HaC4H4O, 
H3C6H6O7 

2 

I 
I 
2 
O 

I 
O 

I 
I 

4 

indicator 
destroyed 

0 
0 
I 

2 
I 
I 
2 
I  dilute 
2 
I  dilute 
2 
2 

I 

2 
2 
I 

2 

I 
2 

3 

2 

I 
I 
2 
O 

0 

2 
2 

2 

I 
I 
2 

O 
I 
O 

2 

I  nearly 
Inearly 
2nearly 

I 
2 

2 
I 

I 
2 
0 

O 

O 
O 

2 

Hydrochloric  .  . 

Nitric      

Thiosulphuric  

Sulphurous  
Hydrosulphuric.  .  . 
Phosphoric    

Arsenic 

Arsenous   .  • 

Nitrous  

Silicic    .  . 

Boric 

Oxalic  

Acetic  

Butyric  • 

Succinic        .  •  .  • 

Lactic.  .  . 

Tartaric  

Citric  

224 


TABLES  AND    TABULAR   SUMMARY 


DIETERICH'S  TABLE  SHOWING  SENSITIVENESS   OF  VARIOUS 
TEST-PAPERS 


Test-papers 

SO, 

HCl 

KOH 

NH, 

Red  

Brazil  Wood  

Cochineal.  ••  .  . 

35  ooo 

35  ooo 

o  ooo 

HaGmatoxylin  .  •  •  •                 •  • 

Huckleberry*  ....         • 

35  °°o 

Litmus    Blue  . 

"         Red 

Phcnolphtalein  ••• 

Rhubarb  

Rosolic  Acid                  .  • 

IO  OOO 

1  5  ooo 

APPENDIX 

ALIZARIN  GREEN   B. 

O.HO.C10H4:NO:C.oH6.S03H 

ALKALIES  =  Green  ACIDS  =»Carmine-red 

Synonym:    Formanek's  Indicator. 

Properties:  Alizarin  Green  B.,  as  furnished  by  Dahl 
&  Co.  of  Barmen,  belongs  to  the  group  of  oxazines 
and  thiazines,  and  forms  a  blackish-green  powder 
quite  readily  soluble  in  water  and  yielding  a  solution 
having  a  dirty-green  color.  It  is  obtained  by  the 
action  of  beta-naphtoquinosulphonic  acid  on  amido- 
naphtolsulphonic  acid  in  alkaline  solution  at  a  high 
temperature.  It  is  more  difficultly  soluble  in  alco- 
hol, yielding  a  flesh- colored  solution.  On  diluting 
the  concentrated  aqueous  solution,  a  flesh-colored 
solution  is  also  afforded.  The  green  color  of  the 
alizarin-green  solution  is  changed  by  diluted  acids 
to  a  carmine-red,  and  restored  by  alkalies  to  green,' 
the  color  changes  being  very  sharp.  The  neutral 
point  is  indicated  by  a  flesh  color. 

Application:  According  to  J.  Formanek,  Alizarin 
Green  B.  is  equal  to  litmus  and  azolitmin  in  sensi- 
tiveness. The  titration  of  carbonates  must  be  car- 
ried out  in  boiling  liquids,  as  with  litmus.  In  the 

225 


226  IN DIC A  TORS 

presence  of  salts  of  ammonium,  aluminium,  and  other 
weak  bases,  the  color-change  is  not  sharp,  just  as  is 
the  case  with  litmus. 

The  indicator  is  also  adapted  for  use  in  the  "dip" 
method  in  the  form  of  test-papers,  which  may  be 
prepared  by  impregnating  filter-paper  either  with 
an  aqueous  solution  of  the  indicator,  in  which  case 
the  paper,  after  drying,  is  flesh-colored ;  or  by  im- 
pregnating the  paper  with  a  solution  rendered  a 
pure  green  color  by  the  cautious  addition  of  an  al- 
kali ;  the  paper  so  obtained  has  a  green  color. 

The  indicator  is  said  to  be  also  well  adapted  for 
use  by  artificial  light. 

Alizarin  Green  G.  exhibits  properties  similar  to 
those  of  Alizarin  Green  B.,  but  it  is  almost  insoluble 
in  alcohol. 

AMMONIACAL   COPPER   SOLUTION 

A  precipitate  of  copper  oxide  indicates  the  end  of  the  reaction 

Preparation:  Dissolve  10  Gm.  of  copper  sulphate  in 
about  500  Cc.  distilled  water, -and  add  ammonia  wa- 
ter, under  constant  stirring,  until  the  precipitate 
first  formed  is  almost  just  dissolved;  then  add  suf- 
ficient distilled  water  to  make  up  the  volume  to 
1000  Cc.  Filter  the  solution,  and  standardize  against 
decinormal  sulphuric  acid. 

Application:  Ammoniacal  copper  solution  is  recom- 
mended by  Elie  Falieres  for  the  titration  of  alkaloids. 
It  is  used  as  follows:  o.  I  Gm.  of  the  alkaloid  is  dis 


CORALL2N-MA  LA  CHITE-GKEEN  227 

solved  in  20  Cc.  of  decinormal  sulphuric  acid,  and 
the  solution  introduced  into  a  cylindrical  jar  placed 
on  a  black  under  ground.  The  copper  solution  is 
then  allowed  to  flow  in  just  until  the  formation  of  a 
persistent,  slight  cloudiness.  The  number  of  Cc.  of 
copper  solution  used  up  represents  only  the  free 
acid ;  this  number  subtracted  from  20,  represents 
the  acid  combined  with  the  alkaloid,  from  which 
the  weight  of  the  latter  may  hence  be  directly  cal- 
culated. 

In  applying  this  method  to  the  titration  of  cin- 
chona barks,  the  author  has  found  that  it  permits  of 
the  titration  of  the  total  alkaloid  in  the  primary  ex- 
tract, as  the  extractive  and  other  matters  present 
are  entirely  without  influence  on  the  visibility  of  the 
precipitate  of  copper  oxide.  The  method  is,  hence, 
useful,  as  it  obviates  the  necessity  for  the  successive 
purification  of  the  extracts  required  when  using 
indicators  giving  color  reactions.  The  method  is 
stated  to  be  applicable  for  all  alkaloids. 

CORALLIN-MALACHITE-GREEN  * 

ALKALIES  =  Purple  ACIDS  =  Green 

Preparation:  According  to  Lachaux,  who  first  intro- 
duced corallin-malachite-green  as  an  indicator  in 
1892,  the  mixture  is  prepared  as  follows: 

*  The  double  zinc-chloride  of  tetramethyl-diparamido-triphenyl- 
carbinol, 


228  INDICATORS 

3.1  Gm.  of  corallin  or  commercial  rosolic  acid  are 
dissolved  in  150  Cc.  of  9O-per-cent.  alcohol,  neutral- 
ized, and  mixed  with  0.5  Gm.  malachite-green  dis- 
solved in  50  Cc.  of  alcohol.  With  this  mixture 
alkalies  give  a  purple  color,  changed  to  green  by 
acids. 

Application :  Malachite-green  dissolves  in  alcohol, 
yielding  a  greenish-blue  solution,  which  possesses 
no  value  as  an  indicator  by  itself,  but  when  mixed 
with  corallin  it  blends  with  the  colors  of  that  in- 
dicator and  renders  the  end  reaction  more  distinct. 
As  only  the  corallin  in  this  mixture  acts  as  an  indi- 
cator, it  follows  that  this  corallin-malachite  green 
mixture  can  be  used  in  titrating  only  those  acids 
and  bases  which  give  a  distinct  end  reaction  with 
corallin  alone. 

E.  S.  Runyon  (Jour.  Amer.  Chem.  Soc.,  XXIII, 
p.  402)  recommends  the  indicator  for  determining 
the  alkali  in  highly  colored  beet  molasses,  as  well 
as  for  determining  the  total  acidity  of  highly  colored 
wines,  vinegars  and  ciders. 

The  method  of  procedure  is  as  follows :  Transfer  10 
Cc.  of  the  sample  to  a  beaker,  dilute  with  about  300 
Cc.  of  boiling  distilled  water,  heat  the  mixture  to 
boiling  for  a  moment  to  expel  all  CO2 ,  cool  to  about 
75°  C.,  add  10  drops  of  the  corallin— malachite-green 
solution,  then  add  an  excess  of  decinormal  NaOH, 
indicated  by  a  purple  color,  titrate  the  excess  of 


DIA  ZOPA  RA  NITKAN1LINE  22Q 

alkali  with  decinormal  acid  solution,  adding  the  acid 
slowly  until  the  appearance  of  a  distinct  green  color. 

The  change  in  color  is  best  observed  by  trans- 
mitted light.  It  is  easier  to  detect  the  transition 
from  the  alkali  to  the  acid  side  than  the  reverse. 

The  results  obtained  with  corallin-malachite-green 
are  invariably  lower  than  those  obtained  with  the 
other  indicators,  but  this  is  to  be  expected,  as  with 
this  indicator  the  titration  is  made  toward  the  acid 
reaction,  and  with  the  other  indicators  it  is  made 
toward  the  alkali  side. 

In  testing  the  sensitiveness  of  the  corallin— mala- 
chite-green, five  drops  of  the  mixture  were  added 
to  100  Cc.  of  distilled  water,  when  o.  I  Cc.  of  centi- 
normal  HC1  or  centinormal  NaOH  was  sufficient 
to  give  a  distinct  acid  or  alkali  reaction.  In  the 
presence  of  other  coloring  matters,  slightly  more  of 
the  standard  solutions  was  required. 

DIAZOPARANITRANILINE-PROPYL- 
METACRESOL 

C,H6N  :  NC6Ha.CH3(OH)CH(CH,)a.CH3  :  OH  :  CH^CH,), 

ALKALIES  =  Pink  ACIDS  =  Faint  Yellow 

Properties  :  Diazoparanitraniline  -  propylmetacresol 
forms  a  powder  insoluble  in  water,  but  soluble  in  a 
dilute  alcohol  containing  30  per  cent,  or  more  of  the 
latter. 

Application :  Diazoparanitraniline-propylmetacresol 
is  stated  by  A.  E.  Sunderland  and  A.  E.  Rhodes  to 


230  2ND  1C  A  TORS 

be  especially  sensitive  to  alkalies,  and  to  be  far 
more  sensitive  than  phenolphtalein,  while  equal  to 
methyl  orange  in  the  estimation  of  ammonia.  It 
can  replace  lacmoid  for  estimating  the  hardness  of 
waters  by  the  alkalimetric  test,  and  can  serve  as 
an  indicator  in  the  titration  of  organic  acids.  Like 
phenolphtalein,  however,  it  is  sensitive  to  carbon 
dioxide  and  carbonates. 

It  is  stated  to  surpass  other  indicators  in  sharp- 
ness of  color-change  (pink  when  alkaline,  to  faint- 
yellowish  when  acid),  as  well  as  in  sensitiveness. 

IRON    ISOPYROTRITARATE 

Fe(C7H7O3)3  +  2H2O 

ALKALIES  =  Orange-red     Acms  =  Violet ;    Colorless 
to  Yellow  with  excess 

Synonym:    Simon's  indicator. 

Preparation:  The  products  of  the  action  of  heat  and 
potassium  bisulphate  on  tartaric  acid  are  distilled 
under  reduced  pressure.  The  brown  viscous  residue 
is  esterified  by  prolonged  boiling  with  alcohol,  the 
pyruvic-  and  pyrotartaric-acid  esters  distilled  off 
under  reduced  pressure,  and  the  residue  finally  dis- 
tilled at  atmospheric  pressure.  A  yellowish  oil 
passes  over,  which  partly  solidifies  on  cooling.  The 
crystalline  product  so  obtained  (about  25  Gm.  from 
25  kilos  of  tartaric  acid)  is  isopyrotritaric  acid,  hav- 
ing a  melting-point  of  164°  C.,  and  resolidifying  at 


IKON  ISOPYKOTR1TARATE  23! 

156°  C.  It  readily  sublimes  in  the  form  of  white 
needles,  which  are  easily  soluble  in  ether  and  in  al- 
cohol, and  less  so  in  water  (1:25  in  boiling  water) 
or  acetic  acid,  are  feebly  acid,  and  have  the  formula 
C7H8O3.  The  potassium  salt,  C7H7O3K.2HaO,  is 
readily  soluble  in  water,  and  the  solution  gives  with 
silver  nitrate  a  yellowish,  gelatinous  precipitate 
which  quickly  blackens.  Its  main  characteristic, 
however,  is  the  intense  violet  color  it  yields  with 
ferric  salts,  and  which  is  of  very  stable  nature,  being 
affected  neither  by  heat  nor  time.  The  iron  com- 
pound is  readily  prepared  from  the  acid  by  digest- 
ing freshly  precipitated  ferric  hydrate  with  a  hot 
saturated  solution  of  the  acid,  and  evaporating  the 
solution  to  dryness  in  vacuo.  It  has  the  formula 
Fe(C,H,08),+  2H,0. 

Properties:  Iron  isopyrotritarate  dissolves  in  water 
affording  a  solution  having  a  red  color  which,  on  the 
addition  of  an  acid,  changes  to  violet,  but  which  is 
discharged  by  an  excess,  and  becomes  orange-red 
to  yellow  on  the  addition  of  an  alkali. 

Application:  The  substance  is  highly  recommended 
as  an  indicator  by  L.  J.  Simon,  who  states  that  the 
color-changes  are  very  sharp.  The  acid  itself  may 
be  advantageously  used  to  indicate  the  presence  of 
ferric  salts,  the  reaction  being  shown  in  neutral  solu- 
tions of  i  :  100000,  and  is  as  delicate  as  that  afforded 
by  potassium  sulphocyanide. 


232  INDICATORS 

IRON   SALICYLATE 

ALKALIES  -  Yellow  ACIDS  -  Red       . 

Synonym:    Wolff's  indicator. 

Preparation  :  The  indicator  is, practically,  a  solution  of 
iron  and  sodium  salicylate,  and  it  may  be  prepared 
thus  :  Dissolve  2  Gm.  of  salicylic  acid  in  10  Cc.  of 
lO-per-cent.  caustic-soda  solution,  and  add  90  Cc. 
water  and  5  Cc.  of  a  solution  of  ferric  chloride  (sp. 
gr.  1.280)  I  part  and  water  19  parts.  The  solu- 
tion is  now  divided  into  two  equal  portions,  to  one 
of  which  just  sufficient  caustic  soda  is  added  to  de- 
velop a  deep-orange  color;  to  the  other  just 
enough  sulphuric  acid. is  added  to  yield  a  red  tint. 
The  two  portions  are  then  mixed,  and  .4  or  5  Gm. 
of  sodium  salicylate  dissolved  in  the  solution. 

Another  method  is  to  dissolve  5  to  6  Gm.  of 
sodium  salicylate  in  25  Cc.  of  water,  add  solution 
of  ferric  chloride  by  drops  until  a  permanent,  slight 
turbidity  appears,  then  filter,  divide  into  two  por- 
tions and  treat  as  above  with  caustic-soda  solution 
and  sulphuric  acid,  and  finally  dissolve  10  Gm.  of 
sodium  salicylate  in  the  mixed  portions. 

Still  another  method  is  to  dissolve  freshly  precip- 
itated ferric  hydrate  to  saturation  in  a  concentrated, 
neutral  solution  of  sodium  salicylate,  by  heating  to 
a  temperature  of  80°  C.,  and  then  filtering.  Of 
the  solution,  from  0.5  to  I  Cc.  is  used  for  each, 
titration. 


IRON  SALJCYLATE  233 

Application:  This  indicator  is  recommended  by  Jules 
Wolff,  who  states  that  it  is  very  sensitive  to  alkalies, 
as  well  as  to  sulphuric,  hydrobromic,  hydriodic,  and 
hydrochloric  acids.  It  is  unaffected  by  phosphoric 
and  hydrofluoric  acids,  as  well  as  by  carbonic,  sul- 
phurous, arsenous,  oxalic,  and  boric  acids.  Ammonium 
salts,  when  present,  have  no  disturbing  action  on 
the  indicator.  The  indicator  is  suitable  for  esti- 
mating the  alkali  in  potassium  and  sodium  carbonates, 
since  it  is  not  affected  by  carbonic  acid.  The  alka- 
line solution  is  yellow,  but  in  proportion  as  car- 
bonic acid  is  evolved,  it  reddens,  and  when  the  acid 
is  present  in  slight  excess,  becomes  reddish-violet 
to  violet.  The  titration  is  considered  to  be  com- 
plete when  only  the  violet  supervenes,  indicating 
that  all  the  alkali  has  been  saturated. 

The  indicator  is  particularly  useful  for  estimating 
boric  acid  in  borates.  For  instance,  20  Cc.  of  a  so- 
lution of  7.387  Gm.  of  borax  in  200  Cc.  water  are 
treated  with  a  known  volume  of  decinormal  sul- 
phuric acid  in  excess,  some  of  the  salicylate  indi- 

*  cator  added,  and  the  free  acid  titrated  with  caustic- 
soda  solution  until  the  violet  tint  is  replaced  by 
orange-red.  The  end  reaction  is  very  sharp,  and 
takes  place  the  moment  when  the  sulphuric  acid  is 
neutralized  by  the  caustic  soda.  The  orange-red 
persists  in  an  excess  of  soda.  If  a  large  excess  of 
sulphuric  acid  is  present,  the  liquid  remains  almost 
colorless  on  the  addition  of  the  indicator,  and  only 


234  IND1CA  TORS 

as  neutralization  proceeds  does  the  violet  color  fi- 
nally develop  and  persist.  The  difference  between 
the  acid  used  and  that  found,  gives  the  equivalent 
of  the  sodium  present.  The  boric  acid  is  then 
found  by  adding  about  20  Cc.  of  glycerin  and  a  few 
drops  of  phenolphtalein  solution.  The  liquid  at 
first  acquires  a  pink  color,  due  to  the  acidity  caused 
by  the  glycerin,  but  soon  becomes  lighter  in  pro- 
portion as  the  caustic-soda  solution  is  added,  until 
the  phenolphtalein  end-reaction  is  observed.  The 
acidity  due  to  the  glycerin  must  be  determined  by 
making  a  blank  titration  using  a  volume  of  water 
similar  to  that  used  in  the  titration,  and  deducting 
the  Cc.  of  alkali  used  from  that  used  in  the  boric- 
acid  titration. 

If  any  ammonium  salt  is  present,  it  is  best  to  add 
excess  of  caustic  soda,  drive  off  the  ammonia  by 
boiling,  and  then  add  excess  of  acid. 

With  calcium  borate,  2.5  Cm.  are  warmed  with 
I  Cc.  of  concentrated  hydrochloric  acid,  and  the 
process  carried  out  as  before. 

If  alumina  is  present,  it  should  be  precipitated 
with  ammonia,  the  ammonia  liberated  and  driven 
off  by  boiling,  and  the  determination  proceeded 
with  as  before. 

The  author  states  that  the  indicator  reaction  is 
very  sensitive  with  decinormal  alkali  or  acid,  one 
drop  of  either  sufficing  to  effect  an  immediate  color 
change. 


PATENT  BLUE  L.  235 

PATENT    BLUE   L. 

ALKALIES  =  Blue  ACIDS  =  Green 

Properties:  Patent  Blue  L.  is  one  of  the  class  of  tri- 
phenylmethane  dyes,  and  is  supplied  by  the  Roche- 
ster Farbwerken.  It  is  neutral  in  reaction  and  sol- 
uble in  water.  The  neutral  and  alkaline  solutions 
are  blue  in  color;  a  slight  excess  of  acid,  however, 
changes  this  to  green. 

Application:  Patent  Blue  L.  is  recommended  as  an 
indicator  for  estimating  the  excess  of  soda  in  bleach- 
ing fluids  prepared  from  chlorinated  lime  and  sodi- 
um carbonate.  One  drop  of  a  i-per-cent  solution 
is  added  to  the  hypochlorite  solution ;  the  latter  is 
then  somewhat  diluted,  and  titrated  with  normal 
acid  in  the  customary  manner.  Other  indicators, 
like  methyl  orange  or  litmus,  are  decomposed  by  so- 
lutions containing  chlorine,  but  this  indicator  is  not. 

PEREZOL 

C,6H19(OH).08 
ALKALIES  =  Pink  to  Mauve  Rose        ACIDS  =  Colorless 

Synonyms:     Pipitzahoic    Acid;    Pipitzahoinic   Acid; 
.  Perezone ;  Von  Duyk's  Indicator. 

Source:  Perezol  is  obtained  from  Pcresia  adnata,  A. 
Gray  (and  various  other  species  cf  Ferezia),  Com- 
posite found  in  Mexico  where  they  are  known  un- 


236  INDICA  TORS 

der  the  name  of  "  pipitzahoac."  The  cylindrical 
rhizomes  of  the  plant  are  about  20  Cm.  long  and  3 
to  4  Mm.  thick,  and  when  dry  are  brownish  exter- 
nally, whitish-yellowish  internally,  and  very  fragile. 
The  fracture  is  fibrous.  Between  the  medulla  and 
the  cortical  layer  is  a  zone  containing  many  orange- 
yellow  specks,  and  in  which  the  perezol  is  localized. 

Perezol  was  discovered  by  Profs.  Altamirano  and 
Armendariz,  of  Mexico,  by  treating  the  coarsely 
comminuted  rhizome  with  benzene  or  toluene,  and 
evaporating  the  solvent  at  a  temperature  of  about 
50°  C.  The  orange -yellow  crystals  are  then  recrys- 
tallized.  The  yield  is  about  5  per  cent. 
Properties:  Perezol,  after  recrystallization,  forms 
odorless,  well- formed  quadrangular  prisms  with 
oblique  terminals,  and  of  orange-yellow  color,  and 
a  persistent  acrid  taste.  Perezol  melts  at  about  103° 
C.,  and  sublimes  at  110°  C.,  yielding  very  deli- 
cate, prismatic  crystals  practically  insoluble  in  cold 
water,  but  slightly  soluble  in  hot  water,  and  quite 
readily  soluble  in  alcohol,  ether,  benzene,  toluene, 
and  oils,  both  fixed  and  volatile. 

With  bases,  even  ammonia  and  metallic  oxides, 
it  yields  violet-black  salts.  Acids  added  to  an 
aqueous  solution  of  an  alkali  pipitzahoate  precip- 
itate the  yellow  pipitzahoic  acid  unchanged. 
Treated  with  reducing  agents,  it  yields  hydroqui- 
none  —  hence  the  name  "  perezone  "  by  which 
it  is  also  designated. 


PEREZOL  237 

Application:  According  to  von  Duyk,  perezol  is  per- 
fectly adapted  for  use  as  an  indicator  because  of  its 
exceedingly  great  sensitiveness  towards  alkalies,  the 
faintest  trace  of  which  suffices  to  afford  a  pink  to 
mauve-red  color.  The  end-reaction  is,  even  with 
ammonia,  instantaneous,  there  being  no  transitional 
stage,  and  is  very  sharp  even  in  extreme  dilutions. 
Dissolved  in  distilled  water,  the  solution  is  faintly 
yellow ;  on  boiling,  a  red  to  mauve  color  develops, 
due  to  the  traces  of  alkali  dissolved  out  from  the 
glass.  One  drop  of  perezol  solution  distinctly  col- 
ors water  containing  one  drop  of  semi-decinormal 
caustic-soda  solution,  or  some  aniline  or  pyridine. 
Potable  waters  acquire  a  mauve-red  color  with 
perezol,  from  the  alkaline-earthy  phosphates  pres- 
ent. Saliva  also  gives  the  reaction. 

For  use  a  I  :  200  alcoholic  solution  is  prepared, 
one  drop  of  which  suffices.  Perezol  is  suitable  for 
titrating  alkaloids  with  which  it  reacts  with  great 
delicacy.  The  indicator  is  not  at  all  influenced  by 
heat.  Solutions  colored  by  alkalies  are  instantly 
decolorized  by  free  acids,  even  carbonic  acid,  as  well 
as  mono-  and  poly-basic  organic  acids.  The  only  ex- 
ception is  ortho-boric  acid  ;  this  acts  like  a  base.  If 
glycerin  be  added  to  the  solution,  however,  the 
boric  acid  behaves  like  other  acids. 

The  mineral  salts  of  the  strong  acids,  as  well  as 
ammoniacal  salts,  are  neutral  towards  the  indicator ; 


238  IN DIC A  7'OXS 

acetates,   bicarbonates,   borates,    and   carbonates    are 
alkaline  towards  it. 

Perezol  is  particularly  adapted  for  estimating  the 
alkalinity,  of  potable  waters,  titrating  alkaloidal  res- 
idues, borax  and  acetates,  etc.  It  is  moreover  suit- 
able for  every  kind  of  alkalimetric  or  acidimetric 
determination.  Its  solubility  in  oils  renders  it, 
besides,  useful  where  ordinary  indicators  are  not 
available. 


POTASSIUM   FERROCYANIDE  WITH 
AMMONIUM   MOLYBDATE 


ATKATTFS-DeColori-      Arm*     Reddish-yellow  *>  dark 

ALKALIES-  ACIDS--    brown  with  excess 


Application:  A  solution  of  the  two  salts  is  used  as  an 
indicator  in  titrating  acids  (mineral,  as  well  as  phos- 
phoric, sulphurous  and  arsenic).  These  afford  a  red- 
dish-yellow reaction  when  present  in  very  small 
quantity ;  with  an  excess  of  acid  a  dark-brown  color 
or  turbidity  is  produced.  On  adding  an  alkali  the 
reddish-yellow  or  dark-brown  color  disappears. 


SODIUM  ALIZARINSULPHONATE  239 

SODIUM   ALIZARINSULPHONATE 

C14H7O4SO8Na 

Red ;   with  ex- 
ALKALIES  =     cess>  yiolet  ACIDS  =:  Yellow 

Synonym:    Alizarin  S. 

Preparation:  Sodium  alizarinsulphonate  is  obtained 
by  the  action  of  fuming  sulphuric  acid  on  alizarin, 
and  conversion  of  the  alizarinsulphonic  acid  into  a 
sodium  salt. 

Properties:  Sodium  alizarinsulphonate  occurs  as  an 
orange-colored  powder  yielding  an  orange  solution. 
The  solution  of  the  indicator  is  rendered  yellow 
by  acids.  Alkalies  in  very  slight  excess  change 
the  color  to  red ;  a  very  large  excess  develops  a 
violet  color. 

Application:  Sodium  alizarinsulphonate  serves  for  es- 
timation of  strong  acids  and  bases.  In  the  presence 
of  free  phosphoric  acid,  as  well  as  acid  phosphates,  the 
indicator  affords  a  yellow  color;  mono-phosphates 
afford  a  red  color,  and  basic  phosphates  a  violet. 
The  color  change  from  yellow  to  red  during  the 
titration  of  phosphoric  acid  is  quite  sharp ;  the 
change  from  red  to  violet,  however,  is  only  very 


240  2ND  1C  A  TORS 

gradual,  and  appears  to  be  due  rather  to  the  increas- 
ing alkalinity  than  to  the  presence  of  neutral  phos- 
phates. The  indicator  has  been  used  for  estimating 
the  acidity  of  urine.  The  process  is  not,  however, 
very  useful,  since  the  color  of  the  urine  itself,  as  well 
as  the  gradual  color  change,  renders  the  observation 
of  the  end-reaction  uncertain. 


INDEX 


PAGl 

Acetates,   cochineal   with 52 

perezol    with 238 

Acid,  acetic,  Congo  red  with 56 

fluorescein    with ., 77 

rosolic  acid  with 156 

anchusic    25 

arsenic,  lacmoid  with 99 

methyl    orange   with 115 

Poirrier  blue  with 136 

arsenous,  lacmoid  with 98 

methyl   orange  with 115 

silver-nitrate  paper  with 214 

phenolphtalein    with 130 

starch    with 163 

boric,  curcuma  paper  with 186 

iron  salicylate  with 233 

phenolphtalein    with 130 

Poirrier  blue  with 136 

carbonic,  alkaline  carmine  solution  with 45 

carminic-acid  with 48 

alpha-napbtolbenzem  with 30 

cochineal    with 52 

curcumin    with 62 

curcumin  W.  with 63 

Congo  red  with 56 

flavescin    with '. 75 

fluorescein    with 77 

gallein   with 82 

241 


242  INDEX 

PAGE 

Acid,  carbonic,  litmus  with 104 

luteol  with 107 

phenol  nitrosylsulphonate  with 126 

phenolphtalein   with 129 

phenolphtalein  paper  with 206 

potassium  hydrorufigallate  with 145 

resazurin    with 150 

rosolic  acid  with *...  156 

tropseolin  OO  with 169 

tropseolin  OOO  with 172 

tropseolin  paper  with 218 

carminic    45 

chromic,  guaiac  paper  with 192 

lacmoid    paper    with 194 

silver-nitrate  paper  with 214 

eupittonic    72 

fuchsine-sulphurous 80 

hydrochloric,  huckleberry  paper  with 195 

phloroglucin-vanillin  paper  with 206 

potassium-sulphocyanate  paper  with...  211 

hydrocyanic,  ferrous-sulphate  paper  with 189 

guaiac-  and  copper-sulphate  paper  with  192 

Poirrier   blue   with 136 

indigosulphonic    88 

indigosulphuric    88 

isopyrotritaric   230 

nitric,  brucine  paper  with 179 

fuchsine    with 180 

lacmoid   with 99 

guaiac  paper  with 192 

nitrophenylic    120 

nitrous,  potassium-iodide  and  starch  paper  with 210 

phosphoric,  cochineal  with S3 

curcuma  paper  with 186 

lacmoid   with 99 

methyl   orange   with.. 115 

potassium    ferricyanide    with 143 

phyllocyanic    - 133 

pipitzahoic   235 

rosolic,   commercial 153 


INDEX  243 

PAGE 

Acid,  salicylic 157 

salts,  tropaeolin  paper  with 218 

santalic    159 

silicic,    lacmoid   with 99 

sulphindigotic    88 

sulphuric,  in  acetic  acid,  methyl  violet  for 119 

Congo  red  with 56 

sulphurous,  alpha-naphtolbenzein  with 30 

brazilin    with 41 

fuchsine   paper  with 193 

iodate  paper  with 197 

starch    with 164 

yellow    D 168 

Acidity,  corallin-malachite-green  for 228 

Acids,  alkaline  carmine  solution  with 45 

alpha-naphtolbenzein    with 30 

benzopurpurine  B,  with 36 

brazilin  paper  with 178 

cochineal    with 52 

Congo   red   with 56 

Congo-red   paper  with 184 

fatty,  curcuma  paper  with 187 

methyl  orange  with 114 

phenolphtalein    with 131 

fuchsine    with 80 

in  alum,  etc.,  ultramarine  paper  with 219 

iodeosine   with 92 

iron   salicylate   with 233 

lacmoid  with 98 

methyl  orange  with 114 

mineral,  alpha-naphtolbenzein  with 30 

flavescin    with 75 

hsematoxylin  paper   with 19  \ 

litmus    with 103 

methyl  orange  with 1 16 

phenol  nitrosylsulphonate  with 126 

organic,  alpha-naphtolbenzei'n  with 30 

cochineal   with 53 

Congo  red  with 57 

curcuma  paper  for 186 


244  INDEX 


Acids,  organic,  diazoparanitraniline-propylmetacresol  with.  230 

flavescin    with 75 

gallein   with 82 

lacmoid   with 99 

litmus    with 105 

methyl  orange  with 114 

perezol    with 237 

phenacetolin   with 124 

phenol  nitrosylsulphonate  with 126 

phenolphtalein  with 131 

tropaeolin  paper  with 218 

perezol   with 237 

potassium    ferrocyanide    and    ammonium    molybdate 

with 238 

phenacetolin    with 123 

resazurin    with 150 

sodium  alizarinsulphonate  with 239 

tropaeolin  OO  with 169 

Albumin,  citric-mercuric-chloride  paper  for 180 

citro-potassium-ferrocyanide  paper  for 181 

citro-sodium-tungstate   paper   for 181 

picro-citric-acid  paper  with 207 

potassio-mercuric-iodide  paper  with 208 

Alcohols,  Poirrier  blue  with 136 

Aldehydes,  fuchsine-sulphurous  acid  with 80 

metaphenylenediamine  hydrochloride  for 133 

Poirrier  blue  with 136 

Alizarin    20 

S 239 

green    B 225 

green  B.  test-paper 226 

green    G 226 

solution    25 

violet    80 

Alkali,  corallin-malachite-green  for 228 

in  soap,  phenolphtalein  for 131 

Alkalies,  alkaline  carmine  solution  with 45 

alkaline  paper  with 176 

alpha-naphtolbenzem   with 30 

benzopurpurine  B.  with 37 


INDEX  245 


Alkalies,  carminic  acid  with 48 

cochineal   with 52 

curcuma  paper  with 186 

diazoparanitraniline-propylmetacres  1  with 230 

fuchsine  with 80 

gallein   with 82 

haematoxylin  paper  with 194 

haematoxylon   with 85 

huckleberry  paper  with 195 

iodeosine  with 92,  94 

iodeosine  G.   with 94 

indigosulphonic  acid  with 88 

iron  salicylate  with . .- 233 

lacmoid   with 98 

litmus  with 103,   104 

perezol    with 237 

phenacetclin  with 123,   124 

phenol   nitrosylsulphonate   with ; 126 

phenolphtalein   with 129 

Poirrier  blue  with 135 

potassium   bichromate   with 140 

potassium  ferricyanide  with 143 

resazurin  with 150 

rosolic  acid  with 155 

tannin  paper  with 217 

Alkaline  carmine  solution 44 

Alkaline  earths,  cochineal  with 52 

Alkaloids,  ammoniacal  copper  sol  tijn  for 226 

brazilin    with 41 

cochineal   with 53 

Congo   red   for 184 

gallein   with 82 

haematoxylin    with 85 

iodeosine  with 93 

litmus   with 105 

methyl  orange  with 1 16 

perezol    with 237 

phenolphtalein   with 130 

Alkanin    25 

paper    176 


246  INDEX 

PACK 

Alkanna   red 25 

Alpha-naphtolbenzem    29 

solution   of 30 

Alpha-naphtol    orange 171 

yellow  I7I 

Althaea   paper 202 

Alumina,  lacmoid  with 99 

Aluminium  salts,  alizarin  green  with 226 

Ammonia,  alkanin  paper  with . .    176 

benzoptirpurine  B.  with 36 

•    benzopurpurin  paper  with 178 

cochineal   with 52 

corallin    with 58 

curcuma  paper  with i85 

curcumin    with 62 

curcumin   W.   with 63 

diazoparanitraniline-propylmetacresol  with 330 

fuchsine    with 80 

fuchsine  paper  with 133 

gallein   with 83 

hsematoxylin  paper  with 1 34 

hasmatoxylon   with 85 

hyacinth  paper  with 195 

huckleberry  paper  with 195 

litmus    with 104 

luteol    with 107 

methyl  orange  with 115 

orange-peel  extract  with 120 

perezol    with 237 

phenacetolin   with 123 

phenol  nitrosylsulphonate  with 126 

phenolphtalein    with 129 

phenolphtalein  paper  with 206 

Poirrier   blue  with 135 

potassium  bichromate  with 140 

rosolic  acid  with 156 

red  cabbage  with 42 

Ammoniacal  copper  solution 226 

Ammonio-ferric   alum 94 

Ammonium  salts,  alizarin  green  with 226 


INDEX  247 

PAGE 

Ammonium  salts,  iron  salicylate  with 233 

methyl  orange  with 114 

perezol   with 237 

rosolic  acid  with 155 

tannin  paper  with 217 

tropseolin   OOO   with 172 

Anchusic    acid 25 

Anchusin    25 

paper    176 

Aniline-azodimethylaniline    65 

Aniline,  Congo  red  with 56 

Congo-red  paper  with 184 

litmus   with 105 

methyl  orange  with 117 

Aniline   red 78 

Anthocyanin    paper 190 

Anthracene    violet 80 

Arsenates,  lacmoid  with 98 

litmus    with 104 

phenacetolin    with 124 

phenolphtalein    with 130 

Poirrier  blue  with 136 

rosolic  acid  with 156 

Arsenites,  lacmoid  paper  with 199 

litmus    with 104 

phenacetolin    with 124 

phenolphtalein    with 130 

rosolic   acid   with 156 

Arsenfuretted  hydrogen,  corrosive-sublimate  pap:r  for 185 

Atlas    orange 170 

Aurin    153 

Aurin    red 153 

Autenrieth's    indicator 106 

Azaleine    78 

Azolitmin    30 

paper 177 

solution    34 

Azoresorcin    149 

paper 211 


248  INDEX 

PACK 

Barium  hydrate  with  carbonate,  phenacefcolin  for 124 

Bases,  sodium  alizarinsulphonate  wkh 239 

Benzaurin    34 

Benzene-azodimethyl-aniline   65 

Benzopurpurin    B 35 

paper    177 

Beta-naphtol    orange I/O 

sulpho-azobenzene    170 

Bicarbonates,  carminic  acid  with 48 

cochineal    with 52 

curcumin   with 62 

curcumin  W.  with 63 

lacmoid  with 98 

methyl  orange  with 1 16 

perezol    with 238 

phenacetolin    with 124 

Poirrier   blue   with 136 

tropaeolin  OO  with 163 

tropseolin  paper  with 218 

Bichromates,  Congo  red  with 57 

lacmoid   with 99 

phenolphtalein    with 130 

Biphosphates,  cochineal  with 53 

Congo  red  with 57 

lacmoid   with 98 

Bismuth  salts,  potassium-iodide  paper  with 210 

Bisulphites,  Congo  red  with 57 

lacmoid   with 98 

Blue    carmine 89 

Blue,    Poirrier,    C4B 135 

Boas'   paper 218 

Boettger's    indicator 54 

ozone  paper 217 

paper 183,  191 

Bolton's    indicator 137 

Borates,  curcuma  paper  with 187 

lacmoid  with 98,  99 

lacmoid  paper  with 199 

litmus   with 104 

methyl  orange  with 116 


INDEX  249 


Berates,  perezol  with 238 

Borax,  curcuma  paper  with 186 

curcumin    with 62 

lacmoid   with 99 

lacmoid  paper  with 98 

perezol    with 238 

phenolphtalein  with 130 

Poirrier  blue  with 136 

Borntrager's   indicator 120 

Brasilin  38 

Brazilin  38 

paper   178 

Brazil-wood  37 

test-solution   7 

Bromeosine   68 

Bromine,  guaiac  paper  with 192 

potassium-iodide  and  starch  p:per  with 210 

Brucine    paper 179 

Buckthorn   paper 179 

Butter-yellow    • 65 

Cabbage,    red •. . . .  41 

tincture    of 41 

Calcium  carbonate,  mesitylene-quinone  for in 

Calcium  hydrate  with  carbonate,  phenacetolin  for 123 

Campeachy   wood 85 

Carbohydrates,   Schiff's  paper  with 214 

Carbon  dioxide,  diazoparanitraniline-propylmetacresol  with.  230 

monoxide,  palladious-chloride  paper  with 205 

Carbonates,  alizarin  green  B.  with 225 

alkaline  carmine  solution  with 44 

alpha-naphtolbenzein    with 29 

cochineal    with 52 

curcuma  paper  with 186 

diazoparanitraniline-propylmetacresol   with 230 

flavescin   with 75 

gallein   with 82 

haematoxylin    with 85 

indigo-sulphonic   acid   with 88 

iron   salicylate   with , , 233 


250  INDEX 

PACK 

Carbonates,  lacmoid  witH 98 

lacmoid  paper  with 98,  199 

litmus    with 103,    104 

methyl  orange 1 16 

perezol  with 238 

phenacetolin  with 123 

phenolphtalein  with %. . . .   120 

phenolphtalein  paper  with 206 

Poirrier  blue  with 135 

potassium   hydrorufigallate  with 144 

rosolic  acid  with 155 

Carmine  42 

paper   .....179 

solution,    alkaline 44 

Carminic    acid  v 45 

Caustic  alkalies  with  flavescin 75 

Cherry    paper 191 

Chloral,   Poirrier  blue  with 136 

Chlorides,  Congo  red  with 57 

lacmoid    with 99 

methyl  orange  with 114 

phenacetolin    with 124 

rosolic    acid    with 155 

Chlorine,  brucine  paper  for 179 

guaiac    paper   with 192 

indigo  carmine  with 90 

potassium-iodide  and  s.arch  paper  with 210 

starch  f or 164 

Chromates,   Congo  red  with 57 

lacmoid    with 99 

lacmoid  paper  with 199 

Chrysaurein    170 

Cider,  corallin-malachit.e-green  with 228 

Cobalt  paper 182 

Cobalt-  and  methylene-blue  paper 182 

Cochineal   49 

paper   183 

tincture,    Luckow's 52 

Cobaltous    nitrate 48 

Colein 54 


INDEX  251 


olein  paper 183 

Color-changes,  sensitiveness  of  operator  to 10 

Common    mallow 108 

Congo   red 55 

paper   184 

solution 57 

Copper,    ammoniacal   solution 226 

Corallin    58 

red  58 

solution    58 

Corallin-malachite-green   227 

Corrosive-sublimate  paper 185 

Citro-mercuric-chloride   papers 180 

molybdic-acid   paper 180 

picric-acid   paper 207 

potassium-ferrocyanide  paper 181 

sodium-tungstate  paper 181 

Cupric  salts,  potassium-ferrocyanide  paper  with 209 

Curcuma  paper 185 

Curcumin   59 

S    62 

W    . 62 

Curcummin    59 

Cyanides,  ferrous-sulphate  paper 189 

Cyanine   63 

reactions  of,  in  acetic-acid  solution 13 

theoretically  considered 16 

Dahlia 118 

paper   «...  190 

Dechan's    indicator 80 

Degener's   indicator 122 

Diamylcyanine   iodide 63 

Dianthine   B 91 

Dianthine  G 93 

Diazoparanitraniline-guaiacol   64 

propylmetcresol    229 

Diazoresorcin   149 

paper   211 

Diethylaniline   orange 71 


252  INDEX 

PACK 

Dieterich's  table,  showing  sensitiveness  of  various  test-papers  224 

Dihydroxyanthraquinone    20 

Diiodofluorescein-sodium    93 

Dimethylamidoazobenzene   65 

solution 66 

Dimethylaniline    orange in 

Dimethyl-paraphenylenediamine  paper 188 

Dioxyanthraquinone    20 

Dioxyphtalophenone    126 

Diphenylamine 67 

orange : 168 

yellow    168 

Direct  violet 118 

Diresorcin-phtalein    75 

Elderberry  paper 188 

Engel  and  Ville's  indicator 135 

Eosine    68 

solution   70 

yellowish    68 

Eosine-methylene   blue 70 

Erythrobenzeine 78 

Erythrosin   B 91 

Erythrosin  G 93 

Ethane,  palladious-chloride  paper  with 205 

Ethyl    orange 71 

solution   72 

Eupitton  72 

Eupittonic  acid 72 

Extract  orange-peel 120 

Fast  yellow 168 

Ferment  paper 189 

Fernambuco  37 

paper   178 

Ferric  salts,  potassium-ferrocyanide  paper  with 209 

potassium-sulphocyanate  paper  with 211 

sodium  salicylate  with : 162 

tannin  paper  with 217 

Ferrous  salts,  ammonio-ferric  alum  with f . . . .    95 


INDEX  253 


Ferrous  salts,  potassium  ferricyanide  with 143 

potassium-ferricyanide  paper  with 209 

potassium  permanganate  with 147 

Ferrous-sulphate  paper 198 

Fittig's  indicator no 

Flavescin  74 

Fliickiger's  sublimate  paper 185 

Fluorescein   75 

solution    77 

Formanek's  indicator 225 

Fuchsiacine 78 

Fuchsine    78 

paper   190 

Fuchsine-sulphurous  acid 80 

Gallein   80 

solution    82 

Galvanometer,  reflecting,  as  an  indicator 147 

Gawalowski's  neutrality  indicator 118 

Gentian  violet  3  B 1 18 

Georgina  paper 190 

Geissler's  test-papers 180 

Glucose,  indigo-carmine  and  sodium-carbonate  papers  with  196 

Schiff's  paper  with 214 

Gold-chloride  paper 191 

Gold  orange in,  170 

Greenwalt's  paper 197 

Guenzburg's  paper 206 

Griess's  red  test-paper 216 

Griess's  yellow  test-paper 203 

Guaiac  paper 192 

Guaiac-  and  copper-sulphate  paper 192 

Haematoxylin    82 

Haematoxylon    85 

paper   193 

tincture   86 

Harmaline    78 

Helianthine in 

paper   204 


254  INDEX 

PAGB 

Herzberg's  paper 184 

Hexa-oxymethylaurin    72 

Hoffmann's  albumin  paper 208 

indicator  72 

Hollyhock   108 

paper  202 

Houzeau's  ozone  paper 194 

Huckleberry  paper 195 

Hyacinth  paper 195 

Hydrogen     dioxide,     dimethylparaphenylenediamine     p  per 

with    188 

potassium  ferricyanide  with 143 

potassium  permanganate  with 147 

tetra  paper  with 217 

Hydrogen  sulphide,  alpha-naphtolbenzein  with 30 

brazilin  with 41 

cochineal  with 52 

Congo  red  with 56 

dimethylparaphenylenediamine    paper 

with    188 

lacmoid  with 98 

lacmoid  paper  with 199 

lead  paper  with 200 

litmus   with 104 

palladious-chloride  paper  with 205 

tropaeolin  OO  with 169 

Hypophosphites,  potassium  permanganate  with 147 

Hyposulphites,  see  Thiosulphates. 

Illuminating  gas,  palladious-chloride  paper  with 205 

Indicator,  ammoniacal  copper  solution  as  an 226 

Autenrieth's   106 

Boettger's   : 54 

Bolton's  138 

Borntrager's    120 

Dechan's   83 

definition  of I 

Degener's 122 

Engel  and  Ville's 135 

Fittig's    • no 


INDEX  255 


Indicator,  Formanek's 225 

Gawalowski's  neutrally 118 

Hoffmann's    72 

Kruger's    75 

Langbeck's  120 

Luck's    126 

Lunge's in,  122 

Lux's  74 

Oser  and  Kalmann's 144 

Pellagri's  133 

Richter's 138 

Schaal's    20 

Simon's    230 

value  of i 

Von  Duyck's 235 

Von  Miiller's i63 

Weiske's    157 

Weselsky's    149 

Wolff's    232 

Zaloziecki  29 

Indicators,  action  cf  in  other  than  aqueous  liquids 12 

application  of 8 

artificial  light  with 10 

characteristics  of 3 

classes  of 3 

correct  choice  of 5 

deterioration  of 9 

dissociation  of 15 

general  considera'kns  of I 

Mohr's  theory  of  the  action  of 19 

object  of I 

observing  color-chrnges  of 10 

requirements  of 2 

see  Table  of  Contents. 

sensitiveness  of  to  acids  and  alkalies,  Tromms- 

dorff's  table,  showing 220 

sodium  flame  for 10 

testing  9 

theory  of  the  action  of 15 

Indigo  carmine 89 


256  INDEX 


Indigo-carmine   paper 196 

and  sodium-carbonate  papers 196 

Indigo  extract 89 

paper  196 

Indigosulphonic  acid 88 

Indigosulphuric  acid 88 

Indigotine  89 

lodate  paper 197 

lodeosine  91 

solution 92 

lodeosine  G 93 

Iodine,  guaiac  paper  with 192 

Iodine,  starch  with 163 

starch  paper  with 215 

starch-  and  ammonium-persulphate  paper  with 216 

potassium-iodide  and  starch  paper  with 210 

zinc-iodide  and  starch  paper  with 219 

zinc-iodide  and  starch  solution  with 173 

Iris  paper 197 

Iron,  isopyrotritarate 230 

salicylate   232 

Iron  and  ammonium  sulphate 91 

Japan  wood 37 

Jaune  d'orient 93 

Kroupa's  parer 190 

Kruger's  indicator 75 

Lacmoid  95 

paper  198 

solution   96 

Lacmus  99 

Langbeck's   indicator 120 

Lead  paper 200 

Lead  salts,  potassium-chromate  paper  with 208 

potassium-iodide  paper  with 210 

Lehman  and  Petri's  dye 125 

Litmus  99 

paper  200 


INDEX  257 


Litmus  paper,  blue  ........................................  201 

neutral    ....................................  201 

red  ........................................  201 

solution    ...........................................  102 

tincture  ...........................................   102 

Logwood   ................................................     85 

Luck's  indicator  ...........................................  126 

Luckow's  cochineal  tincture  ...............................     52 

Lunge's  indicator  ......................................  in,  .122 

Luteol   .................................  ,  .................  106 

solution    ............................................  108 

Lutke's  paper  .............................................  218 

Lux's  indicator  ............................................     74 

Magenta  .................................................     78 

Mallow    .........  *  .........................................   108 

paper  .............................................  202 

Mandarin  G.  extra  .....  ..................................  .   170 

Mandarin  orange  ........  .  .................................  in 

Manganous-acetate  paper  ..................................  203 

Manganous-chloride  paper  .................................  203 

Mann's  paper  .............................................   180 

Mercuric-chloride  pr.per  ...................................   185 

Merget's  paper  ............................................  '  205 

Mesitylene-quinone   .......................................  no 

Metadiamidobenzene    .....................................   132 

Metallic  salts,  white-lead  paper  with  .......................  219 

Metals,  cobalt-  and  methylene-blue  paper  with  .............   182 

Metaphenylenediamine    ...................................   132 

paper  ..............................  203 

solution    ...........................   133 

Methane,  palladious-chloride  paper  with  ...................  205 

Methylaniline   violet  .....  ..................................  1  18 

Methyl  orange  ............................................   in 

differentiating  from  other  oranges  ..........   112 

paper   .....................................  205 

reaction  of,  in  acetic-acid  solution  ..........     13 

solution   ......................  .............  113 

theoretically  considered  .....................     18. 

Methyl-orange  and  phenolphtalein  solution  ................  118 


258  INDEX 

PAGk 

Methyl  violet 118 

Milk,  neutrality  of,  litmus  for  showing 105 

Mineral  salts,  perezol  with 237 

Mineral  waters,  potassium  hydrorufigallate  for 144 

Mohr's  mechanical  theory  of  affinity 19 

Molasses,  beet,  corallin-malachite-green  with 228 

Musculus'  paper 189 

Naphtolbenzein,   alpha- 29 

sclution  of 30 

Naphtol  orange 171 

Negative  electrical  current,  pole-reagent  paper  for  showing  207 

Neutral  cobalt  r.  itrate 48 

Neutral  potassium  chromate 140 

Neutral  red 167 

New  yellow *. 168 

Nitrates,  diphenylamine  with 68 

Congo  red  with 57 

methyl  orange  with 114 

phenacetolin  with 12  j. 

rosolic  acid  with 155 

Nitrites,  indigo  carmine  with 90 

metaphenylenediamine    with 132 

metaphenylenediamine  paper  with 205 

methyl  orange  with 115 

sulphanilic-acid    and    alpha-naphtylamine-sulphate 

paper  with 216 

Nitrophenylic  acid 120 

Normal  cobalt  nitrate 48 

CEnokrine  paper 204 

Oliver's  albumin  paper 181,  207 

Oliver's  glucose  papers \tf 

Oliver's  tungstate  paper 181 

Orange  I 17 v 

Orange  II 170 

Orange  III ill 

Orange  IV 168 

Orange  A 170 

Orange  B 171 


INDEX  259 


range  extra 170 

Orange  G.  S 168 

Orange  M 168 

Orange  N 168 

Orange-peel  extract 120 

Organic  bases,  Congo-red  paper  with 184 

Oser  and  Kalmann's  indicator 144 

Oxalates,  potassium  permanganate  with 147 

Oxychlordiphenylquinoxaline   106 

Oxygen,  atmospheric,  alkaline  carmine  solution  with 44 

indigo-carmine  with 90 

indigo-carmine  paper  for 196 

nascent,  manganous-chloride  paper  for 203 

Oxy-isoxyloquinone   no 

Oxymeta-xyloquinone   no 

Ozone,  dimethylparaphenylenediamine  paper  with 188 

Iguaiac  paper  with 192 
Houzeau's  p  per  for 194 
manganous-acetate  paper  with 203 
palladious-chloride  paper  with 205 
paper 191,  217 
potassium-iodide  and  starch  paper  with 200 
tetra  paper  with 217 
thallous-hydrate  paper  with : ..  218 

Palladious-chloride  paper 205 

Para-nitrcphenol   120 

theoretically  considered 16 

Para-rosolic  acid 153 

Paris  violet 1 18 

Patent  Blue  L 235 

Pellagri's  indicator 133 

Perezol  235 

Perezone   235 

Pernambuco  37 

paper   178 

Phenacetolin   122 

Phenolbenzem   34 

Phenol  nifrosylsulphonate 125 

Phenolphtalein  126 


260  INDEX 

PAGE 

Phenolphtalein   paper 206 

solution    128 

reaction  of  in  acetone  solution 13 

theoretically    considered 17 

Phenolphtalein  and  methyl-orange  solution 118 

Phenols,  Poirrier  blue  for 136 

Phenylenediamine,  meta-   132 

solution    133 

Phosphates,  Congo  red  with 57 

curcuma  paper  with 187 

curcumin  with 62 

lacmoid  with 98 

litmus  with 104 

phenolphtalein  with 130 

Poirrier  blue  with 136 

sodium  alizarinsulphonate  with 239 

Phosphorus,  silver-nitrate  paper  with 214 

Phyllocyanic   acid 133 

Phyllocyanin   133 

solution    134 

Phloroglucin-vanillin  paper 206 

Picro-citric-acid  paper 207 

Pittakal  72 

Pine  wood,  tetra  paper  with 217 

Poirrier  blue,  €46 135 

Poirrier's   orange 1 1 1 

Pole-reagent  paper 207 

Polka  paper 219 

Polysulphide  solution 137 

Potassio-ferric   cyanide 142 

Potassio-mercuric-iodide  paper 208 

Potassium  anhydrochromate 138 

bichromate    138 

solution 139 

chromate  140 

paper   208 

solution  142 

dichromate 138 

ferricyanide    142 

paper   209 


INDEX  26l 


'otassium  ferrocyanide  paper 209 

with  ammonium  molybdate 238 

hydrate  with  carbonates,  phenace  olin  fDr 123 

hydro rufigallate    ' 144 

hypermanganate    145 

iodide,  starch-  and  ammonium-persulphate  paper 

with    .- 216 

pnper 210 

and  starch  paper 210 

monochromate   140 

oxymanganate  145 

permanganate   145 

sulphocyanate  paper 211 

supermanganate   145 

Pseudalkannin  25 

Pyoktanin   118 

Pyrogallol  phta'ein 83 

Pyrosine    B 91 

Pyrosine  J 93 

Quinoline   blue 63 

litmus  fcr 105 

methyl  orange  with 117 

Red  cabbage 41 

Red  potassium  chromaie 138 

Red  prussiate  potash 142 

Red- wood   37 

Reflecting  galvanometer  as  an  indicator 147 

Resazoin 149 

Resazurin  149 

paper    211 

solution    150 

Resorcinbenzein 151 

Resorcin  blue 95 

Resorcin,  Poirrier  blue  with 136 

Resorcin-phtalein    75 

Rhubarb  paper 212 

Richter's    indicator 138 

Riegel's  paper 184 


262 


Riegler's  indicator 64 

Rosaniline  hydrochloric^ 78 

paper  190 

Rose  coloring-matter 152 

Rose  paper 213 

Roseine 78 

Rosolic  acid,  commercial 153 

paper 213 

Rubin  78 

Rubianite   78 

Salicylic  acid 157 

solution 159 

Santalic  acid 159 

Santalin 159 

Sapan  wood 37 

Schaal's  indicator 20 

SchifFs  paper 213,  214 

Schonbein's  hydrocyanic-acid  paper 192 

Schonbein's  ozone  paper 210 

Schonbein  and  Pagenstecher's  paper 192 

Schott's  paper 219 

Selle's  paper 195 

Sensitiveness  of  operator  to  certain  colors 10 

Serum  paper 214 

Silicates,  curcuma  paper  with 187 

curcumin  wilh 62 

lacmoid  with 98 

lacmoid  paper  with 98,  199 

litmus  with 104 

methyl  orange  with 116 

Silver-nitrate  paper 214 

Silver  salts,  ammonio-ferric  alum  with 95 

potassium-chromate  paper  with 208 

potassium  iodide  paper  with 210 

Simon's    indicator 230 

Soda,  patent  blue  L.  with 235 

Soda  in  soap,  methyl  orange  for 117 

Soda  with  alumina,  methyl  orange  for 117 

Sodium,  alizarinsulphonate 239 


INDEX  203 

PACK 

Sodium,  azoxystilbene-disulphonate 62 

alpha-naphtolazobenzene   sulphonate 171 

borate,  with  resazurin 150 

carbonate  with  acetate,  methyl  orange  for 117 

diethylamidoazobenzene  su  phonate 71 

diethylanilineazobenzene  sulphonate 71 

dimethylamidoazobenzene-sulphonate  in 

dimethylanilineazobenzene-sulphonate in 

diphenyl-diazobinaphtionate    55 

flame  105 

hydrate  with  carbonate,  phenacetolin  for 123 

indigotin-sulphonate   89 

orthotolidine-disazobinaphtylamine-sulphonate   ....     35 

parasulphobenzene  azodimethylaniline in 

phosphate,  cochineal  with 52 

salicylate   162 

tetrazodiphenyl-naphtiona'e    55 

Soluble  indigo 89 

Solferino   78 

Solution,  alizarin 25 

alphanaphtolbenzein    30 

azolitmin 34 

carmine  alkaline 44 

Congo  red 57 

corallin    58 

dimethylamidoazobenzene   66 

cosine  7° 

ethyl  orange 72 

fluorescein   77 

gallein   82 

iodeosine  92 

lacmoid  96 

litmus   102 

luteol   108 

metaphenylenediamine    133 

methyl   orange 113 

methyl  orange  and  phenolphtalein 118 

orange-peel  ex!  ract 120 

phenolphtalein  128 

phyllocyanin 134 


264  INDEX 


Solution,   polysulphide > 137 

potassium  bichromate 139 

potassium  chromate 142 

potassium  ferricyanide 143 

resazurin  150 

salicylic  acid 159 

tropaeolin  OO 169 

zinc-iodide  and  starch 172 

Spring- water,  mesitylenequinone  with in 

metaphenylenediamine  for 133 

paranitrophenol  with 121 

Stahl's  paper 182 

Starch    162 

paper   215 

solution    164 

Starch-  and  ammonium-persulphate  paper 215 

Stevenin's  paper 202 

Storch's  indicator 62 

Sugar,  indigo-carmine  paper  with 196 

Sulphanilic-acid  and  alphanaphtylamine-sulphate  paper 216 

Sulphates,  Congo  red  with 57 

curcumin  with 62 

lacmoid  with 99 

litmus  with 104 

methyl  orange  with 114 

phenacetolin  with 124 

rosolic  acid  with 155 

Sulphides,  cochineal  with 52 

curcuma  paper  with 186 

curcumin  with 62 

lead  paper  with 200 

lacmoid  with 99 

litmus  with 104 

lacmoid  paper  with 199 

methyl  orange  with 1 16 

phenacetolin  with 123 

phenolphtalein  with 130 

rosolic  acid  with 156 

Sulphindigotic  acid 88 

Sulphites,  cochineal  with 53 


INDEX  265 

PACK 

Sulphites,  Congo  red  with 57 

curcuma  paper  with 187 

curcumin  with 62 

lacmoid  with 99 

lacmoid  with 98 

lacmoid  paper  with 199 

litmus  with 104 

methyl  orange  with 115 

phenacetolin  with 124 

phenolphtalein  with 130 

starch  with ._ 164 

Sulphoazobenzene-alphanaphtol  171 

betanaphtol  170 

Sulphur,  potassium  permanganate  for 147 

Sun  yellow 62 

Table,    Dieterich's,   showing  sensitiveness   cf  various   test- 
papers    224 

Thomson's,   showing  hydrogen   atoms   replaced   by 

NaOH  or  KOH 223 

Trommsdorff's,  showing  sensitiveness  of  indicators 

to  acids  and  alkalies 220 

Tannin,  indigo  carmine  with 90 

paper 216 

Test-papers,  general  remarks 174 

preparation  of 175 

preservation  of 176 

see  Table  of  Contents. 

table    showing   sensitiveness    of    various,    Die- 
terich's    224 

Test  solution,  Brazil-wood 37 

Tetra  paper 217 

Tetrabromeosine    68 

Tetrabromphenolphtalein    165 

Tetrabromoresorcinphtalein  68 

Tetraiodofluorescein   :. 91 

Tetramethylparaphenylenediamine   paper 217 

Tetra-oxyphtalophenone 75 

Thallium-hydroxide  paper 217 

Thallous-hydrate  paper 217 


266  INDEX 


Theory  of  color-changes,  Mohr's 19 

Thiosulphates,  curcuma  paper  with 187 

curcumin  with 6a 

lacmoid  with 99 

methyl  orange  with 115 

potassium  permanganate  with 147 

starch  with 164 

Thomson's    table    showing    hydrogen    atoms    replaced    by 

NaOH  or  KOH 223 

Thymolphtalein    166 

Tincture,  Brazil-wood 37 

cochineal,  Luckow's 52 

haematoxylon  86 

litmus  102 

red-cabbage 41 

Toluidine,  Congo  red  with 56 

litmus  with 105 

methyl  orange  with 117 

Toluylene  red 167 

Trimethylbenzene-quinone  no 

Trommsdorff's  table  showing  sensitiveness  of  indicators  to 

acids  and  alkalies 220 

Tropaeolin  D in 

paper  204 

OO 168 

solution   169 

OOO  No.  1 170 

OOO  No.  II 171 

paper    218 

Turmeric  yellow 59 

Turpentine,  dimethylparaphenylenediamine  paper  with 188 

tetra  paper  with 217 

Ultramarine  paper 218 

Uranine   75 

Urea,  ferment  paper  with 189 

Uric  acid,  silver-nitrate  paper  with 215 

Vinegar,  corallin-malachite-green  with 228 

Von  Duyk's  indicator 235 


INDEX  267 


Von  Miiller's  indicator 168,  171 

Weiske's  indicator , 157 

Well-water,  nicsitylene-quinone  with in 

metaphenylenediamine  with 133 

paranitrophenol  with 121 

Weselsky's  indicator 149 

paper   211 

White-lead  paper 219 

Witz's  test 118 

Wolff's  indicator 232 

Wood-pulp,  dimethylparaphenylenediamine  paper  with 188 

Wurster's  ozone  paper 217 

red  ozone  paper 188 

Yellow  potassium  chromate 140 

Zaloziecki's  indicator 29 

Zinc,  cochineal  paper  for 183 

Zinc,  cobaltous  nitrate  and  potassium  ferrocyanidc  with 49 

Zinc-iodide  and  starch  paper 219 

solution 172 


